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LIFE SCIENCES STUDY GUIDE Grade 11

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Life Sciences

Study guide

Grade 11

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Study Guide G11 ~ Life Sciences

CONTENTS STRAND 1: DIVERSITY, CHANGE AND CONTINUITY. ............................................... 3 UNIT 1: UNIT 2: UNIT 3: UNIT 4: UNIT 5: UNIT 6: UNIT 7: UNIT 8: UNIT 9: UNIT 10: UNIT 11: UNIT 12: UNIT 13: UNIT 14: UNIT 15: UNIT 16: UNIT 17: UNIT 18: UNIT 19:

Biodiversity and classification of micro-organisms ......................................... 4 Viruses and bacteria ....................................................................................... 8 Fungi ............................................................................................................ 21 Protista ......................................................................................................... 31 Diseases caused by micro-organisms .......................................................... 45 The prevention and treatment of diseases ................................................... 55 Biodiversity of plants..................................................................................... 60 Bryophytes (Mosses) .................................................................................... 63 Pteridophytes (Ferns) ................................................................................... 69 Gymnospermae (Naked seeds) .................................................................... 75 Angiosperms (Flowering plants) ................................................................... 81 The significance of seeds ............................................................................. 89 Biodiversity of animals .................................................................................. 94 Porifera and Cnidaria.................................................................................. 100 Platyhelminthes .......................................................................................... 104 Annelida ..................................................................................................... 108 Arthropoda .................................................................................................. 113 Chordata ..................................................................................................... 117 Role of invertebrates in agriculture and ecosystems .................................. 121

STRAND 2: LIFE PROCESSES IN PLANTS AND ANIMALS ................................... 124 UNIT 1: UNIT 2: UNIT 3: UNIT 4: UNIT 5: UNIT 6: UNIT 7: UNIT 8:

Photosynthesis ........................................................................................... 125 Animal nutrition – Mammals ....................................................................... 140 Chemical digestion and absorption............................................................. 158 The relationships between food intake, energy, growth and health requirements .............................................................................................. 166 Tooth decay and drug abuse ...................................................................... 179 Cellular respiration...................................................................................... 187 Gaseous exchange..................................................................................... 200 Excretion by humans ................................................................................. 219

STRAND 3: ENVIRONMENTAL STUDIES..................................................................232 UNIT 1: UNIT 2:

Population ecology ..................................................................................... 233 Human impact on the environment ............................................................. 257

REFERENCES:........................................................................................................... 282

Study Guide G11 ~ Life Sciences

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STRAND 1: DIVERSITY, CHANGE AND CONTINUITY

Life consists of a wide variety of organisms that live in a variety of niches. This strand introduces learners to different life forms ranging from micro-organisms to macroscopic plants and animals. They are organised according to a manmade classification system that is based on the visible features. The role of organisms in an ecosystem will be discovered, including micro-organisms that are the main cause of diseases. This strand also includes the evolutionary development of plant- and animal phyla. In this strand you will study the following: • The basic structure and general characteristics of viruses, bacteria, fungi and protista. • The role of micro-organisms in maintaining balance in the environment. • Symbiotic relationships such as nitrogen fixing bacteria in plants and E.Coli in the human intestines. • The effect and management of one disease from each of the four groups of micro-organisms. • The immune response of plants and animals against the infecting microorganisms as well as vaccinations. • The use of medication such as antibiotics and the effect of them on microorganisms. • The use of micro-organisms to produce medicine. • The traditional use of technology to produce beer, wine and cheese. • The grouping of Bryophytes, Pteridophytes, Gymnosperms and Angiosperms in accordance with the presence or absence of vascular tissue, true leaves and roots, seeds or spores and fruit. • Asexual and sexual reproduction in plants. • The biodiversity of invertebrate animals

Study Guide G11 ~ Life Sciences

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UNIT 1: BIODIVERSITY AND CLASSIFICATION OF MICROORGANISMS There are a large number of living organisms. The number of species on earth today varies from as little as three million to a 100 million or more. Living organisms are divided into two main groups, plants and animals.

What do you know? You already know that organisms consist of cells. The simplest organisms consist of single cells and complex organisms consist of many cells.

What do you have to know? The use of the electron microscope has discovered two types of cellular organisms: prokaryotes and eukaryotes. The prokaryotes have very small cells with no true nucleus. The eukaryotes have a true nucleus that is separated by a membrane from the cytoplasm.

Challenge! 1. Which micro-organisms are both beneficial and essential for our survival? 2. Which micro-organisms are responsible for our deaths?

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Living organisms are classified into five groups. The main kingdoms are: ♣ Monera ♣ Protista ♣ Fungi ♣ Plantae (plant kingdom) ♣ Animalia (animal kingdom)

Did you know? If only one page were to be used to describe every specie, then it would have covered a total of 6,03 km of book shelving

Micro-organisms refer to those organisms that cannot be seen with the naked eye. This includes examples of all the Prokaryotes, some Protozoa and Fungi, as well as viruses. Even though micro-organisms share the feature of being small organisms, they have little in common and differ greatly in structure and function. Did you know? You cannot see the Micro-organisms vary in structure and function. Micromillions of virusses organisms can be both beneficial and harmful to the and bacteria leave environment. Decomposition and recycling is necessary your nose everytime for life. Micro-organisms benefit man economically in the you sneeze. Flu, production of bread, wine, beer and cheese. pneumonia and even tuberculosis can Micro-organisms cause diseases such as cholera, yellow spread by sneezing. fever, malaria, tuberculosis, flu and Aids. They are the cause of diseases in plants and play a role in the spoiling of food. The name “prokaryotes” is derived from the Greek word pro (which means before) and karyon (which means core/nucleus). These organisms are characterised by the absence of a true core (nucleus) in cells. The use of the electron microscope indicates that the cells of the prokaryotes: • do not have a distinct nucleus. • have a single round chromosome composed of DNA in the cytoplasm. • do not have mitochondria, chloroplasts or structured flagellae. • contain a cell wall composed of a compound from a protein-like origin. • are extremely small. (1 to 10 μm in diameter). Prokaryotes

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The name is derived from the Greek word eu (good) and karyon (nucleus). This group includes the fungi, plants and animals. The electron microscope has made it possible to observe the following features of eukaryotes: • The cell has a nucleus that is separated from the cytoplasm by a nuclear membrane. • The nucleus contains chromosomes. • The cytoplasm contains membrane bound structures called organelles such as endoplasmic reticula and mitochondria. • Some cells have flagellae or cilia. • When a cell wall is present it usually consists of cellulose and/or chitin. • Cells are 10 to 100 μm in diameter. Eukaryotes

The prokaryotes and simple eukaryotes

Kingdom Monera

This kingdom consists of all bacteria and cianobacteria. The genetic material of these organisms consists of circular DNA that is unprotected in the cytoplasm. The cytoplasm contains a few organelles. Not one of these organelles is surrounded by a double membrane, as in the eukaryotes. The cell wall is a firm structure, consisting of polysaccharides. Some organelles have the ability to convert atmospheric nitrogen to organic compounds. More about Monera: • These organisms are mostly prokaryotes, because they do not have a true nucleus. Nutrition takes place through absorption or photosynthesis. Monera do not reproduce sexually. • Bacteria are the best known example of this kingdom which was discovered in 1676 by Anton van Leeuwenhoek. They are microscopic and the cell is surrounded by a cell wall. Many bacteria secrete mucus that forms an external sheath around the cell. Some forms move using flagellae while other small forms move passively in water or air. • Bacteria are unicellular. • Reproduction is asexual by a process known as binary fission where the cells divide into two or through conjugation those results in genetic recombination. • Bacteria are widely spread in nature. They are found in air, water, soil, in or on food, within or on the bodies of organisms and in sewage. • Bacteria decompose dead organisms to prevent the build-up of these organisms. They also play an important role in the maintaining of soil fertility in the nitrogen cycle. • Some bacteria are pathogenic and cause diseases such as tuberculosis in humans, spleen sickness in cows and rotting in plants.

Study Guide G11 ~ Life Sciences

Kingdom Protista

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This kingdom consists of unicellular eukaryotes and the multi-cellular organisms that are closely related to them.

The sub-kingdom, Protozoa, consists of a large variety of small, eukaryotic organisms. Most of them are unicellular, animal-like organisms. Nutrition is mostly heterotrophic. Most protozoa are parasitic. Organisms that are parasitic feed off living organisms. They have complicated life cycles that include more than one host. Plasmodium falciparum is a protozoan that causes malaria in humans and uses the adult mosquito as a vector. Fig.1.1.The following diagram indicates the distribution of malaria in the world.

TEST YOUR KNOWLEDGE! 1. What are micro-organisms? 1) 2. Discuss the ecological and economic importance of micro-organisms. (7) 3. In table form name the two kingdoms under which micro-organisms are classified and give two differences between the organisms in each of the kingdoms. (6) [14]

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UNIT 2: VIRUSES AND BACTERIA What do you know? You should know by now that viruses and bacteria are microscopic organisms that can cause disease.

What should you know? In this unit you will learn about: • The adaptation of viruses and bacteria to their environment and their diversity. • The necessity of virus and bacteria to the environment.

Challenge: 1. Do some research using reputable resources on diseases people can contract from viruses. 2. Name the viral diseases plants are susceptible to? 3. What diseases can animals contract from viruses? 4. What human diseases are caused by bacteria? 5. What diseases can animals contract from bacteria? 6. Name the bacterial diseases plants are susceptible to? 7. What benefit do bacteria have on the ecosystem?

VIRUSES • • •

Studying viruses will enable you to:

Discover the structure and biological importance of viruses. Find out about the replication of viruses. Learn about the general characteristics of viruses.

Remember: Viruses have a very simple structure. They are dependent on plant, animal or bacterial cells for their survival. They often cause disease. They are extremely small – between 10 nm and 200 nm. Do you know what a nanometre (nm) is? If you don’t know, look it up and write it in your exercise book.

Structure of viruses:

Viruses usually are rod-shaped or spherical in shape with a large number of triangular facets on the surface. They are often symmetrical. Viruses contain a nucleic acid enclosed within a protein coat or capsid. In plant viruses the nucleic acid is usually RNA, and in animal viruses the nucleic acid could either be RNA or DNA, but never both.

Did you know? Viral diseases of plants are usually carried by insects, but also by contaminated shears and other garden tools.

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The only life function of a virus is reproduction. A virus cannot be regarded as a cell, as it does not have a nucleus with chromosome material, it does not feed, it does not move, and there is no regulation of osmosis or exchange of gases. Therefore it is regarded as non-living.

The external structure of a bacteriophage (left) and an influenza virus (right)

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Fig 1.2: The external structure of a bacteriophage (left) and an influenza virus (right) Fig 1.3: The Rota virus Activity: Look up the definition of the words “cylindrical”, “spherical” and “symmetrical" in a dictionary.

Find out: What is a pathogen and a vector?

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Biological importance of viruses

“Virus” is a Latin word for “poison”. Viruses cause disease and are therefore the main pathogens of plants as well as animals and humans. They are host specific. The virus could even be tissue specific within the same organism, for example the polio-virus only affects the nerve tissue, but not the intestines. Viruses are obligate parasites that replicate within their host cells by changing the nucleic acid of the host cell to that of their own, and cause the host cell to die. Since viruses reproduce within host cells, it is very difficult to control them. Antibiotics do not work, and vaccines aren’t always successful, therefore, the best way to control viruses is by prevention. Viruses can spread from one person to the next through direct contact, sneezing, coughing or vectors. Fig. 1.4: The MI-virus Tip: When a plant is affected by a virus, remove the contaminated plant material to avoid further contamination, as there are no antidotes against viral infections.

The spread of viruses:

Replication of viruses:

Viruses can spread through food, by direct contact or through carriers/vectors.

Viruses replicate within living cells only. A virus that replicates within bacteria is termed a bacteriophage.

A bacteriophage attaches itself firmly to the wall of a single bacterial cell or bacterium (attachment), thereafter the nucleic acid content of the bacteriophage is injected into the cell (insertion), leaving the capsid behind. The DNA of the bacterium is used to replicate the viral DNA and form proteins for the new capsids (latent phase). When many bacteriophages have formed, the wall of the bacterium bursts releasing the new bacteriophages (lysis).

General Characteristics of viruses: • • • •

A virus contains either DNA or RNA. Viruses cannot grow or replicate by cell division Viruses are obligate parasites, using living host cells to generate new viruses. A virus is host-specific and can even be tissue-specific.

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BACTERIA Do it yourself! To examine bacteria cultures you will require the following apparatus: • nutrient agar (feeding agar) • 250 ml conical flask • a pressure cooker • sterilised Petri dishes • cotton wool and aluminium foil • sterile wire loops Fig. 1.5: Apparatus for activity

Conical flask

Petri dish

Fig. 1.6: Microbiological loop

Tip: You can make your own sterile wireloop by bending a loop in nichrome wire, and sticking the other end into a wooden handle.

Mix of 40g nutrient agar in water. Pour the mixture into the conical flask. Close the neck of the flask with cotton wool and cover it with aluminium foil. Sterilise the mixture by boiling it in the pressure cooker for 15 minutes. Gently lift the aluminium foil and remove the cotton wool. Pour the mixture into the base of the petri dish and cover with the top half. Allow the medium to cool. You now have a medium on which bacteria can be cultivated. Sterilise the microbiological loop by heating it with a Bunsen burner. Dip the loop into a liquid or scrape it across any surface to pick up bacteria. Open the petri dish for approximately 20 seconds and scrape the loop across the agar medium. Find a clean location, where you expect to find little or no bacteria and scrape the microbiological loop across the surface. Use another petri dish to scrape the loop across the agar medium. Label the petri dishes and store in a dark place or inside a cupboard for a few days.

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Remove the petri dishes after a few days and examine them. What do you observe? Are some of the dishes clean? What can you deduce from this?

What have you discovered?

Beware! Some bacteria can be dangerous, and you should handle the petri dishes with great care! When you have completed your examination, you have to decontaminate your Petri dishes and its content by sterilising it in a pressure cooker.

Bacteria are microscopic, single-celled organisms, varying in size from 5 µm to 1 µm, that reproduce quickly and form visible colonies.

Structure of bacteria:

Every bacterial cell is surrounded by a cell wall consisting of polysaccharides. The cell wall is enveloped by a capsule or slimy sheath. The cell content is a mass of grainy protoplasm, contained within its membrane. Bacteria are prokaryotes, meaning that they do not have a true nucleus. The cell has whole strands of DNA called a nucleoid. Small circular pieces of DNA called plasmids float around in the cytoplasm. Bacterial cells have nutrient granules of fats, proteins and glycogen in the protoplasm, and are generally colourless, although some can be coloured.

Fig. 1.7: The structure of a bacteriophage

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Fig 1.8: Line diagram of a bacterium cell.

A – pili C – capsule E – flagellum G – vacuole I – nucleoid

B – ribosome D – cell wall F – cytoplasm H – plasmid J - cytoplasmic membrane

Some bacteria move around using flagella, which are long, thin hair-like fibrils. Bacteria are classified according to their shape, namely bacilli (rod-shaped), cocci (spherical or ellipsoid), vibrio (comma-shaped) and spirillium (spiral-shaped). •

Bacteria are able to reproduce in various ways, for example budding, spore form, segmentation, conjugation (temporary fusion), and binary fission (asexual reproduction).

•

Bacteria reproduce asexually when conditions are favourable. These conditions include the availability of enough food and water, it is dark and the temperature is optimal.

•

During binary fission the DNA duplicates and divides into two and moves apart.

•

A membrane forms across the middle of the cell to separate the cytoplasm. A new cell wall develops on the cell membrane.

•

Binary fission can happen every 20 to 30 minutes.

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Fig. 1.9: The life cycle of a bacteriophage

Fig. 1.10: Various forms of bacterial cells

A. Bacilli (rod-shaped) B. Cocci (Round-shaped) C. Cocci in bundles D. Cocci in pairs E. Spirillium (spiral-shaped) F. Vibrio (Comma-shaped)

Ecological importance of bacteria: Pathogenic bacteria:

The word pathogen comes from the Greek words “pathos” meaning suffering and “genesis” that means origin. A pathogen therefore relates to the origin of diseases. Pathogenic bacteria, in other words, are bacteria that cause disease.

Did you know? The chronic Respiratory Disease in chickens is caused by Mycoplasma gallisepticum, causing gurgling sounds when chickens go to sleep. A chicken that recovers from this disease remains a carrier of the disease and it could be present in the eggs of infected hens, and the day-old chickens.

Disease causing bacteria can be controlled by using antibiotics manufactured from certain fungi and bacteria. Most antibiotics,

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however, do not kill bacteria, but inhibit the production of proteins that form the bacteria. Broad-spectrum antibiotics are nonspecific and kill many different types of bacteria. Did you know? The bacteria Narrow-specific antibiotics will only kill specific causing bacterial wilt in pathogens. potatoes, beans and tomatoes, (Pseudomonas), can stay active Pathogenic bacteria penetrate the body in various ways. Diseases like tuberculosis, pneumonia and in the ground for years, and diphtheria spread through the air and when an increase the spread of the infected person coughs, sneezes or spits the disease during wet weather. disease can be spread. The bacteria block the tissue that transports water inside Food poisoning (botulism), gastro-enteritis and cholera are transmitted through food and water that the plant, and the plant starts comes in contact with contaminated faeces, or to wilt. through flies that pass the bacteria on from contaminated faeces to food. To prevent these diseases, water should be kept clean, and drinking water should be boiled. All vegetables and fruit should be washed. Did you know? Corynebacterium species, that cause abscesses in sheep, cattle and goats are transmitted through contaminated shears, filthy shearing pens, contaminated clothing of shearers, contaminated dipping troughs and so forth and can penetrate their bodies through lesions caused by tick bites, thistles, and thorns from trees, castration and even the umbilical cords of new-born lambs.

Bacteria causing tetanus, boils, abscesses and acne, can penetrate the body through lesions of the skin. Your skin should be washed regularly and wounds should be disinfected to prevent the spread of these bacteria. Diseases like bubonic plague are transmitted by vectors such as fleas on rats.

Venereal diseases like syphilis and gonorrhoea are transmitted by sexual contact. These and other similar diseases can be prevented through a chaste lifestyle as intended by our Creator. Conversely there are good bacteria like decomposition bacteria in the ground which are responsible for breaking down dead plant and animal material. Even in food bacteria could be beneficial, like in the production of cheese, yoghurt, vinegar, sauerkraut and gherkins by means of fermentation. Bacteria also play a significant role in the manufacture of silage. Some bacteria live symbiotically with other organisms. Various mutualistic bacteria can be found, such as nitrogen-fixing bacteria in the nodules on the roots of legumes, as well as rumen bacteria in ruminants that provide vitamin B12 to the animal.

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Escherichia coli is a rod-shaped bactarial cell living in the colon of homoiothermic animals, such as mammals. On an average scale, about 100 miliard to a 100 billion of this bacteria is excreted by the human and if E. Coli (the used abbreviation) is found in water, it is an indication that the water is infected with excrement (faeces). E. coli in the human digestive system

Figure 1.11: E. coli The E. Coli produces vitamin K which is necessary for blood clotting. E. coli as a cause of disease Escherichia coli may not be harmful, but if this bacteria is found in the wrong part of the body, it can be very dangerous:

•

• If a hole forms in the colon, the sterile abdominal cavity can be infected by E.coli bacteria. A serious and potential life threatening sickness, peritonitis, can develop. Usually an emergency operation will take place where the abdominal cavity is rinsed and the patient is treated with antibiotics. If the urinary tube is infected with colon bacteria, a urinary infection can develop.

General Characteristics of bacteria: Bacteria are prokaryotic and the simplest of microbial cells. Other general characteristics are that they are tiny and have distinctive cell walls. They lack a true nucleus and the DNA is free floating. Role in biotechnology

Due to the long history in laboratorial cultures and the ease with which these bacteria can be manipulated, E. coli plays an important role in current biotechnology. E. coli is a versatile organism and is a good host for the production of various proteins. Scientists can transfer genes of other micro-organisms to these bacteria with the help of plasmids, in order to generate large amounts of proteins with the help of the fermentation process. One of the first usable applications of this recombination DNA technology, was the manipulating of E. coli to produce the human insulin hormone.

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The genetic amending of E. coli is used in the development of vaccines and in bioremediation (the use of micro-organisms to remove pollutants). With the help of classic micro-biology, these bacteria are also used as an indicator in the food industry. A high concentration of E. coli in a product indicates that the product may contain other pathogens.

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Terminology: Agar: a gel made of red-algae used for biological cultures Antibiotic: organic compounds formed by micro-organisms that prevent the growth of other micro-organisms. Antibody: a protein produced by white blood cells that destroys or neutralises an antigen. Antigen: a protein in the capsid/coat of a virus or bacterium that causes the white blood cells to produce antibodies. Attachment: the adherence of a virus to the host cell. Autotrophic bacteria: a bacterium that produces its own food. Bacteria: unicellular micro-organisms without a true nucleus, thus it is prokaryotic. Bacteriophage: a virus that penetrates certain bacteria and destroys the bacterial cell during replication. Conjugation: the temporary fusion of two unicellular organisms so that they may exchange core material before they divide. Heterotrophic bacteria: bacteria that is dependent on other organisms for their food. Immune: a natural resistance to a particular infection. Infect: affect a person with a micro-organism that causes disease. Lymphocyte: a type of white blood cell. Lysis: rupture of a bacterium wall to release bacteriophages. Mutualistic bacteria: a bacterium that lives with another organism from whom it feeds, but both the organisms benefit. Pandemic: a worldwide epidemic. Parasitic bacterium: a bacterium that gets its food from a living host. Pathogen: an organism that causes disease. Prokaryotic: organisms without a true nucleus such as bacteria. Protein: complex organic compound synthesised by the combination of amino acids. Spore: a bacterium with a protective protein wall. Sputum: a mixture of saliva and mucus coughed up from the respiratory tract. Vaccine: an antigenic preparation which stimulates the production of antibodies to provide immunity to one or more diseases. Vector: an organism, usually an insect, which transmits a disease or parasite from one organism to another. Virus: a non-cellular, non-living, disease causing particle that consists of genetic material (DNA or RNA) and a protein capsule.

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TEST YOUR KNOWLEDGE! Choose the correct answer to the questions below. Write the appropriate letter opposite the question number in your exercise book. 1.

Which of the following is not a characteristic of a virus? A an obligate parasite B replicates within a living cell C consists of RNA or DNA D nucleus surrounded by a protein sheath.

What does a virus consist of? A nucleic acid and protein

protein and cellulose

nuclei and cytoplasm

RNA and DNA

Viruses are all … A pathogenic and single-celled

prokaryotes

cellular in structure

non-living and non-cellular

Which one of the following characteristics of viruses is not of biological significance? A they are main pathogens in humans. B

they play an important role in decomposition.

they are obligate parasites.

they replicate inside living host-cells only.

Why are viruses regarded as pathogens? A they cause disease. B

they replicate inside living host-cells.

they are difficult to control.

they are obligate parasites.

Which one of the following is a characteristic of viruses? A they can be found in water only. B

they are living single-celled organisms.

they cause diseases.

they cause deterioration of food.

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A characteristic of bacteria is A they usually contain chlorophyll. B

they contain no nucleic material.

they need light to grow.

they have a cell wall.

Which of the following is not a characteristic of bacteria? A some are saprophytes and others autotrophic. B

a nuclear membrane surrounds the nucleus.

they have cell membranes.

they are single-celled prokaryotes.

Why are some bacteria referred to as pathogens? A they feed off dead organisms. B

they are prokaryotic organisms.

they live symbiotically inside the intestines of mammals.

they cause disease. (9)

Answer the following questions: 2.1.

2.9.

What protein is produced when a virus enters animal tissue, that inhibits the replication of the virus? What independent and individual genetic unit appears in the form of a DNAring inside a bacterium? What is an insect called that transmits pathogenic bacteria from one host to another? What single-celled organisms can be found in the form of coccus, spirillum and bacillus? What is the relationship between different living organisms called where both benefit from it? What organism consists of a nucleic acid surrounded by a protein coat? What substance can be found in the centre of a virus? What disease-causing bodies, smaller than bacteria, replicate within a living host cell only? What acellular structure is neither plant nor animal? (9)

3. 4. 5. 6. 7.

Describe the structure of viruses. Why are viruses harmful to living organisms? In what ways do viruses spread? Why are bacteria called prokaryotic organisms? Name the different forms of bacteria.

2.2. 2.3. 2.4. 2.5. 2.6. 2.7. 2.8.

(6) (4) (4) (2) (4)

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Draw a labelled sketch of a bacterial cell. (10) Under which conditions do bacteria reproduce asexually? (3) Describe the reproduction of bacteria in suitable conditions. (6) Describe the ways in which bacteria can spread to humans, name the diseases which spread this way and how the spread of these diseases can be prevented. (29) Discuss, in detail, the ecological importance of bacteria? (12) Bacteria are able to reproduce very rapidly if environmental conditions are favourable. The table shows how rapidly bacteria are able to reproduce over a period of three hours.

12. 13.

Time in 20 minutes Number 8 of bacteria

14.

100

120

140

160

180

128

256

512

1024

2048

a) Plot a line graph to show the growth of bacteria over a period of three hours. (10) b) What happens to the number of bacteria after each 20-minute interval?(2) c) Name the process causing the increase in the number of bacteria. Briefly, explain this process. (4) d) What would happen to the number of bacteria if you heated the culture for 15 minutes, at a temperature of 60°C? Give a reason for your answer. (3) If you have flu and your mother sends you to school because you have to write an examination, how would you ensure that you do not infect other learners around you? (3) [120]

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UNIT 3: FUNGI What do you know? You already know that a fungus is a plant with the body called a mycelium consisting of hyphae, and no roots, stems or leaves are present. Since it does not have chlorophyll, it cannot metabolise sugars and starches using sunlight. It reproduces by means of spores formed in sporangia.

What you will learn? In this unit you will: • Learn about the structure, nutrition and reproduction of fungi. • Cultivate fungi. • Discover the ecological and economical value of fungi.

Challenge: 1. What cancer-causing toxin, recently in the news, is produced by the fungus Aspergillus flavus in peanuts (as well as wheat and maize)? 2. What diseases can a human contract from fungi? 3. What plant diseases are caused by fungi? 4. What diseases can animals contract from fungi? 5. Most of us eat fungi with our staple diet. Name the fungus. 6. What important role do fungi play in medical science? 7. If you compare the value of fungi (economical, industrial, as well as in the gastric system), against its detrimental effects (deterioration of food, and other materials and diseases), would the world be a better place without fungi? Give a reason for your answer.

Do it yourself! Look up the meaning of the words heterotrophic, saprophytic and parasitic and record them in your exercise book. Cultivate your own fungi by placing a piece of moist bread in a plastic bag and store it in a dark, warm place for a few days. What do you notice after a few days? You can do the same with a piece of pumpkin, cheese, or any other piece of food. Where do you think the spores come from, that grow on the food? You can now grow single cultures of fungi in the same way you did with bacteria in the previous unit. If you have access to a microscope, you can examine the hyphae you have cultivated. Use a dissecting needle to transfer the hyphae onto a glass slide and examine under the microscope. There may be sporangia present on the specimen. You may use photo-micrographic slides to study the fungi. These can be found on the Internet.

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What have you discovered? Fungi, a part of the botanical group called Mycophytes, differ from other plant groups, as they are heterotrophic due to the lack of chlorophyll. They can be saprophytic or parasitic. Mycophytes can be single-celled or filamentous. An example of a Mycophyte we will study in this unit is black bread mould or Rhizopus Stolonifer. Fungi are present in virtually any possible ecological habitat and live in a variety of growth media, such as ground, air, water, plants, animals, plastic, chemicals, and many other moist organic materials. The Rhizopus species is visible as a fine downy growth commonly found on food such as bread, cake or fruit that has been stored in a closed container or plastic bag. Habitat

Bread mould has a vegetative plant body consisting of branched, Did you know? The colourless filaments (hyphae), entwined and matted fungus I’kowa together called a mycelium. The mycelium grows (Termitomyces partly inside the substrate and a partly on top of the umkowaani), can grow substrate. The hyphae growing across the surface of the substrate are called stolons. Hyphae that grow up to 250 mm in into the substrate are called rhizoids. The hyphae of diameter and always bread mould are known as coenocytes (“see-nogrows close to termite sites”), as they mounds after rains have no internal Did you know? There (October to March) cross walls (nonseptated), while are a number of and nowhere else. the hyphae of different types of fungi, other moulds can for example toad stools, be septated but not branched. The cytoplasm mushrooms, mildew and inside the hyphae contains many small nuclei blight. (multinucleate). There are also reserve nutrients such as lipids and glycogen present in the cytoplasm. The cell walls of most moulds consist of chitin. Structure

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Fig. 1.12 General structure of fungus

cap

spores

hypha

Gills

Annulus

Stalk/stem

basidiocarp

mycelium

As mentioned before, all fungi are heterotrophic, as it takes its carbohydrates from the substrate it grows on. Black bread mould is a saprophyte, as it lives off dead organic material. The enzyme diastase breaks down starches outside the fungal filaments to simple sugars like glucose, which are absorbed along with other salts by the hyphae (mainly rhizoids), and are synthesised in the protoplasm to other organic compounds such as proteins. Nutrition

Reproduction

Black bread mould reproduces both sexually and asexually.

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Fig. 1.13: Life cycle of Rhizopus stolonifer (black bread mold)

Under suitable conditions, groups of hyphae grow upwards from the substrate. These hyphae are known as sporangiophores (sporangia carriers). At the end of a sporangiophore, cytoplasm and nuclei gather together and swell to form a sporangium. A convex membrane called a columella forms inside the sporangium and separates the content of the sporangium from the rest of the sporangiophore. Cytoplasm and a number of nuclei group together and a membrane forms around them to form multinucleate spores. The rest of the protoplasm, not involved in the formation of spores, absorbs water and exerts pressure on the sporangium causing it to burst open and release the spores. The spores are transmitted by wind, water or direct contact. Asexual reproduction

Sexual reproduction heterothallic

fungal

Sexual reproduction occurs during unsuitable environmental conditions (dry and cool), by two filaments (morphologically similar, but physiologically

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differentiated into two mating types; + and -) that form short branches sideways towards each other. Due to the density of the cytoplasm, with numerous haploid nuclei, the ends of the filaments swell to form progametangia. A transverse membrane forms, which separates the suspensor from the gametangium. Where the gametangia touch, the membranes dissolve, and numerous + and – nuclei fuse in pairs. A zygote with numerous diploid zygote nuclei forms. The wall of the zygote thickens, and becomes prickly and darker in colour and the zygote becomes a zygospore. After a resting period, the content of the zygospore divides by meiosis, the wall breaks open, and a new hypha, called the promycelium grows upwards. At the top end of the promycelium a sporangium forms with spores. The spores are dispersed when the sporangium bursts. The spores will germinate if they land on a suitable substrate.

General Characteristics of fungi The Fungi are eukaryotes, which may exist in nature as either single or multi-celled organisms or in both at different points in the life cycle. Fungi are avascular i.e., no specialised respiratory, digestive or transport systems beyond the hyphae themselves. Most fungi grow as tubular filaments called hyphae. A connected mass of hyphae is a mycelium. Fungi have a vegetative body called a thallus, composed of hyphae. Motile Fungi contain Flagella, which is either whiplash or tinsel type. The walls of hyphae are often reinforced with chitin, a polymer of N-acetyl glucosamine and Cellulose. Fungi have small nuclei with very little repetitive DNA. Fungi are never autotrophs, and are usually found either as opportunistic saprophytes (living on dead organic matter) or in some parasitic or symbiotic relationship with plants or other autotrophs. Food reserves stores as glycogen (like animals), not starch (like plants). Spores may be either sexual or asexual. Fungi reproduce by means of spores, budding, or fragmentation.

Ecological and economic role of fungi

Fungi, along with bacteria, play an important role in the break down and decay of dead animal and plant material. Can you imagine what would happen if there were no Did you know? The use of fungi? Draw up a table to compare the antibiotics was discovered in advantages and disadvantages of the decomposing process of fungi. 1928 by the English microbiologist, Alexander Fungi also play an important economic Fleming. role in various areas. Crops can be destroyed by fungi; causing large financial losses. The financial losses caused by parasitical fungi on animals are much smaller than on plants. In humans, fungi can cause oral thrush, athlete’s foot and other skin infections.

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Another ecological role of fungi is the symbiotic relationship with algae to form lichens. The fungus obtains nutrients from the algae and the fungus supplies the algae with inorganic nutrients. This is called mutualism. Another mutualistic relationship is that of fungal threads called mycorrhizae, growing on roots of trees. The fungal threads obtain organic foodstuffs from the tree and in return absorb water and mineral salts for the tree.

What do you know now? Fungi are non-photosynthetic organisms, of which most are saprophytic, living on dead organic material. Some fungi are parasitic. Mycelium growth is characteristic of fungi. Fungi reproduce asexually, by means of spores, and sexually. Fungi are of great importance in certain commercial processes, such as the manufacturing of alcoholic beverages, some food types, antibiotics and other products. Fungi are also pathogenic, and play an essential role in the decomposition of organic waste.

Fig. 1.14: Lichen on the trunk of a karee tree

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Terminology: Aerobic: the presence of oxygen. Anaerobic: the absence of oxygen. Chitin: the substance the cell walls of fungi and the exoskeleton of Arthropods consist of. Columella: a dome-shaped cross wall separating the sporangium from the sporangiophore. Decomposer: an organism that breaks down dead organic matter. Desiccation: the removal of water from a structure. Eukaryote: an organism with a nucleus and organelles in the cell. Extracellular digestion: digestion that occur outside the cell. The cell secretes enzymes and absorbs the products of digestion through the cell membrane. Fungi (mycophytes): a group of thallus plants that do not contain chlorophyll and cannot photosynthesise and are therefore heterotrophic organisms. The reproduction organs (Gametangia and sporangia) are always unicellular. Gametangium: a structure that produces gametes. Heterothallic: different individual and physiological thallus plant bodies (+ and -). Heterotrophic: an organism that cannot produce its own food. Host: the organism on or in which a parasite lives. Hypha: a fungal thread. Humus: nutritious material formed by rotten leaves and other material in the ground. Lichen: an organism consisting of a fungus component and an algae component. Mutualism (mutualistic): a symbiotic relationship whereby both the organisms benefit. Mycelium: a mass of hyphae forming a plant body. Mycorrhiza: a fungus living symbiotically with the roots of plants. Parasite: an organism that lives on and off another organism. Pathogen: an organism that causes disease. Pro-gametangium: a short outgrowth in mouldy bread which forms a gametangium. Promycelium: mycelium that grows from a zygospore. Rhizoid: hyphae in fungi which grow into substrate for attachment and absorption. Saprophytic (saprophyte): an organism that lives off dead organic matter Septum: a cross wall. Sporangiophore: hyphae in fungi that grow vertically from the substrate and produce sporangia. Sporangium: a structure in which spores are formed. Spore: an asexual reproductive cell. Thallus: a plant body that can be uni- or multicellular and where no stems, leaves or roots can be distinguished. Zygospore: a thick walled spore, in rest, that is formed when the content of two gametangia fuse together.