Seeds and seed dispersal KS4

Seeds and seed germination

Seeds  Seeds come in many shapes and sizes and each have methods of germination which suit them best. It’s important to understand what your seed is and what its needs to have the best chance of growing into a healthy plant  Seeds are the product of plants successfully reproducing after having being fertilized by pollen from plants of their own variety.  The process of a seed growing into a plant is called germination. The conditions needed to successfully germinate must be met otherwise the new plant will fail to germinate successfully or not grow at all until the ideal conditions are met.  Plants have evolved many ways of seed dispersal (How they spread their seeds)

Anatomy of a seed Tesla: It is the outer coat of the seed that protects the embryonic plant.

Micropyle: It is a tiny pore in the testa that lies on the opposite of the tip of the radicle. It permits water to enter the embryo before active germination Cotyledon: In some plants, this contains high quantities of starch and will provide a source of food for the developing embryo prior to germination Radicle: This is the embryonic root which will develop into the primary root of the plant. It is usually the first part of the embryo to push its way out of the seed during germination An epicotyl is important for the beginning stages of a plant's life. It is the region of a seedling stem above the stalks of the seed leaves of an embryo plant. It grows rapidly

How are seeds made?  Plants produce flowers to make seeds. To make a seed a flower must be pollinated. Pollen from the male part of one flower travels to the female part of another flower where the seeds are made. Most, but not all plants, have both male and female parts inside one flower  There are many things the help with pollination, these are animals such as insects, birds, and bats; water; wind; and even plants themselves.  What insects can you think of that help with pollinating plants?

Plant reproduction Structure

Function

Sepals

Protect the unopened flower

Petals

May be brightly coloured to attract insects

Stamens

The male parts of the flower (each consists of an anther held up on a filament)

Anthers

Produce male sex cells (pollen grains)

Stigma

The top of the female part of the flower which collects pollen grains

Ovary

Produces the female sex cells (contained in the ovules)

Nectary

Produce a sugary solution called nectar, which attracts insects

Seed dispersal  Seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants are not able to move around so have to rely upon a variety of dispersal methods to disperse seeds.  Dispersal of seeds is very important for the survival of plant species.

If plants grow too closely together, they have to compete for light, water and nutrients from the soil. Seed dispersal allows plants to spread out from a wide area and avoid competing with one another for the same resources  The 5 methods of seed dispersal are by gravity, water, explosive action, wind and by animals

Seed dispersal by water  Seeds dispersed by water are contained in light and buoyant fruit, giving them the ability to float. Coconuts are well known for their ability to float on water to reach land where they can germinate. Similarly, willow and silver birches produce lightweight fruit that can float on water

Seed dispersal by explosive action  Some plants distribute their seeds by violently ejecting them so that they fall well away from the parent plant. This is explosive dispersal  Some plants like the Hura crepitans, commonly called the dynamite tree due to the sound of the fruit exploding, the explosions are powerful enough to throw the seed up to 100 meters.  If you would like to see a video of plants dispersing their seeds via the explosive method then copy and paste the following link into your web browser. https://www.youtube.com/watch?v=OB0P3mx_lxY

Seed dispersal by animals  Animals disperse seeds in several ways. First, some plants, like the burr at left, have barbs or other structures that get tangled in animal fur or feathers, and are then carried to new sites. Other plants produce their seeds inside fleshy fruits that then get eaten be an animal. The fruit is digested by the animal, but the seeds pass through the digestive tract, and are dropped in other locations. Some animals bury seeds, like squirrels with acorns, to save for later, but may not return to get the seed. It can grow into a new plant

Seed dispersal by wind  Seeds from plants like dandelions are light and have feathery bristles and can be carried long distances by the wind. ... To help their chances that at least some of the seeds land in a place suitable for growth, these plants have to produce lots of seeds  Some tall trees produce seeds with stiff wings covering the seed that enable them to fly long distances. The wings are twisted and balanced so that the seed spins around as it is carried along by the wind. These natural adaptations for using the wind to transport the weight of the seed must be technically accurate, as the wings of modern planes and helicopters are designed in the same way

Seed dispersal by gravity  The plant use of gravity for dispersal is a simple means of achieving seed dispersal. The effect of gravity on heavier fruits causes them to fall from the plant when ripe. Fruits exhibiting this type of dispersal include apples, coconuts and passionfruit and those with harder shells (which often roll away from the plant to gain more distance). Gravity dispersal also allows for later transmission by water or animal.

Conditions needed to germinate  All seeds need water, oxygen, and proper temperature in order to germinate. Some seeds require proper light also. When a seed is exposed to the proper conditions, water and oxygen are taken in through the seed coat.  Some seeds require light to germinate while others do not. When sowing seeds its always important to research what will best suit your seeds during germinating.

Why is water needed when germinating seeds?  Seeds absorb water, after absorbing enough water, the embryo bursts the seed's outer shell and the small, growing plant emerges.  Seeds need water so that they can absorb nutrients and minerals (These help the plant grow healthily) from soil.  The first sign of germination is the absorption of lots of water, activating the functions needed for germination and growth. After absorbing enough water, the embryo grows too large for the seed and bursts the outer shell; a small plant emerges.

Why is oxygen needed when germinating seeds?  Seeds absorb the water around them which makes the coat of the seed swell. Oxygen is required by the germinating seed as the main source of its energy during germination.  Therefore it is important to allow for adequate flow of air (oxygen) to get to your seeds when sowed. This means they should left somewhere with as much air as possible without sacrificing the other needed conditions for germination.

Why does temperature matter when germinating seeds?  One of the biggest factors that affects the success, efficiency, and speed of seed germination is temperature.  Germination relies on a number of chemical and physical reactions within the seed, and the speed and success of those reactions is highly temperature dependent.  Respiration, where the seed breaks down stored carbohydrates for energy, is probably the most notable process involved that is temperature dependent.

If germination happens too slowly then the seeds may run out of the energy stores needed to begin growing a plant.  The optimal temperature is the one at which germination is the fastest. Slower germination speeds increase the days to emergence for the seeds, which in turns means that the seeds and seedlings have a greater chance of failure  Where do you think you could put seeds in your house that would meet all these requirements for seeds germination?

The effects of ideal growing conditions ď‚´ Seeds will not grow (stay dormant) until the ideal germination conditions are met. We can see this clearly in nature.

The picture on the left is of the Atacama Desert in Chile before rain, the picture on the right is taken in the same place but after rainfall. The seeds in the soil waited until the conditions were met to successfully germinate and grow into the plants you see.

The stages of germination  Step 1: Water fills the seed and begins to swell.  Step 2: The water activates enzymes that begin the plant's growth.  Step 3: The seed grows a root to access water underground which absorbs more water, minerals and nutrients from the soil.  Step 4: The seed grows shoots that grow towards the sun to begin turning the suns energy into food (photosynthesis).

 To see a time-lapse video of a seed germinating and growing into a plant copy the link below into your web browser. youtube.com/watch?v=w77zPAtVTuI

Seeds in the land based sectors  During the Level 1 Btec Land Based Studies you need to explore the many land based sectors. Seeds are used by a wide variety of land based sectors and without seeds we wouldn’t be able to not only eat the vegetables and fruits we eat now but it would also impact the meat we eat as well.  There are two main types of farming  Arable - Arable farming involves growing crops such as wheat and barley rather than keeping animals or growing fruit and vegetables. Arable land is land that is used for arable farming. Farmers need to buy seed in bulk so they can fill their fields with crops to sell to make a wide variety of products.  What household food items can you find that contain either Wheat or Barley?

Seeds in the land based sectors  The second main type of faming is pastoral  Pastoral farming is aimed at producing livestock, rather than growing crops.

Examples include dairy farming, raising beef cattle, and raising sheep for wool.  Although pastoral farmers raise animals to provide food, clothingand many other resources from animals they still rely on whatis grown from seed.

Commercial grains farmers feed to cows are often composed of corn, oats, barley or a mixture. While barley is the least expensive, oats are often the preferred grains because they are easily digested by cattle due to the high fibre content

Gardening and landscaping ď‚´ Gardeners and landscapers need a good knowledge of seeds and plants as their jobs will often include the sowing, growing and planting of various species of trees and plants. They may need to be considerate of seed dispersal and will have to be aware of what conditions are required for strong and healthy growth.

ď‚´ Can you think if any other jobs in the land based sector that require the use of seeds?