Questions 1.3 What is a binomial, and what does it tell you about an organism? 1.4 Explain how the skin covering of a reptile differs from that of an amphibian. 1.5 State two characteristics that all arthropods have in common. 1.6 State two characteristics that differ between insects and arachnids.
1.7
Flowering
plants
may
be
monocots
or
dicots. Plants are organisms that have cells with cell walls made of cellulose (section 2.4). At least some parts of a plant are green. The green colour is caused by a pigment called chlorophyll, which absorbs energy from sunlight. The plant uses this energy to make glucose, using carbon dioxide and water from its environment. This is called photosynthesis. Plants include small organisms such as mosses, as well as ferns and flowering plants. Figure 1.10 shows the classification of flowering plants. They are split into two groups, the monocotyledonous plants – usually known as monocots – and the dicotyledonous plants, known as dicots.
S
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Phylum Flowering plants
Characteristics: l have roots, stems and leaves l have xylem and phloem l reproduce by producing seeds l
seeds
produced
inside
ovary,
inside
fl
ower. Monocotyledonous plants: l have strap-shaped leaves with parallel veins l have one cotyledon inside each seed. Dicotyledonous plants: l have leaves which can be broad, and which have a network of branching veins l have two cotyledons inside each seed. pea Pisum sativum
corn Zea mays
parallel veins strap-shaped leaves broad leaves
1.8
Viruses
are
not
true
living
things. You have almost certainly had an illness caused by a virus. Viruses cause common diseases such as colds and influenza, and also more serious ones such as AIDS. Viruses are not normally considered to be alive, because they cannot do anything other than just exist, until they get inside a living cell. They then take over the cell’s machinery to make multiple copies of themselves. These new viruses burst out of the cell and invade others, where the process is repeated. The host cell is usually killed when this happens. Figure 1.11 shows one kind of virus. It is not made of a cell – it is simply a piece of RNA surrounded by some protein molecules. It is hugely magnified in this diagram. The scale bar represents a length of 10 nanometres. One nanometre is 1 × 10–6 mm. In other words, you could line up more than 15 000 of these viruses between two of the millimetre marks on your ruler.
network of branching veins Figure 1.10 Classifi
cation
of
fl
owering
plants.
S protein
nucleic acid (RNA)
10 nm Figure 1.11 An
infl
uenza
virus.
Chapter 1 Classifi
cation 9
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