All living things need to produce more of their own kind to replace ones that die.
Flowering plants reproduce by making seeds.
Before a seed can grow into a new plant they have to be fertilized by pollen.
Pollen comes from another plant during a process called pollination.
Pollination and fertilization take place in the flower of the plant.
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Petals: Brightly coloured. They are used to attract insects by their bright colour and scent.
Sepals: Green leaves around the outside of the flower. Sepals are usually smaller than the petals,. Used to protect the flower while it is still in bud. Stamens: This is where pollen is made Carpel: The carpel is the green stalk in the middle of the flower. |
Sexual reproduction in a flowering plant has FOUR main stages
- Pollination: This is when pollen lands on a new flower
- Fertilization: This is when the pollen and the seed meet
- Seed dispersal: This is when the seed is spread around, away from the plant that made it
- Germination : This is when the seed, having reached the ground, starts to grow into a new plant
Pollination
A plant is pollinated when pollen from another flower reaches it.
Pollen is a yellow dust and it has to reach the stigma of the plant being pollinated.
The pollen has to be carried from the stamen of one flower to the stigma of another.
It is usually carried by bees (or other small animals) but it can be carried by the wind.
Fertilization
After pollination fertilization takes place. This is when the pollen and the ovule join together to make a seed.
The seed also contains a food store, usually starch.
The part of the flower surrounding the seed is known as the fruit.
A berry is the fruit of a plant. Berries will contain the seeds needed for the next generation of plants.
After fertilization the petals and stamens wither and die. The ovary (which forms the fruit) swells up, sometimes considerably. (ie as in the apple)
Seed dispersal
The job of the fruit is to carry the seeds as far as possible from the parent plant so the new plants have room to grow and do not compete for resources such as light, water and nutrients in the soil.
This process is called seed dispersal.
A plant will disperse their seeds four main ways:
1. The fruit is eaten by animals such as birds but are not digested. The seeds pass out the animal along with its droppings eg cherry, blackberry. These fruits look and taste nice.
2. The fruit splits open. sometimes this happens with a lot of force and the seeds are shot out. eg beans. the pod is the fruit and the beans are the seeds.
3. The fruits have little hooks. these hooks stick to the fur of animals. eg burdock.
4. The fruits have wings or hairs and this lets them get carried by the wind,. eg sycamore trees have winged fruits.
Germination is the process by which the seed actually starts to grow.
Conditions needed for germination
Water Oxygen and Warmth
The seed will not germinate untill it gets warm.
As well as warmth the seed also needs oxygen and water to grow.
Without all three (Water, oxygen and warmth) the seed will not grow.
The germination period is time between planting and starting to germinate.
Experiment to show how warmth effects the germination period
Three small pots had damp cotton wool placed in the base, with three bean seeds placed on each piece of cotton wool.
The pots were placed at the following locations:
- A warm, brightly lit window-sill,
- a closed refrigerator
- a warm dark airing cupboard.
The seeds were inspected and watered every day.
The time taken to germinate was recorded in each case.
Conditions:
Window-sill: warmth, light and water
warm, dark cupboard: warm, no light and water
Refrigerator: cold, no light and water;
Results
The seeds in the refrigerator took the longest to germinate (8 days)
The seeds on the window-sill and the seeds in the cupboard germnated quickly (3days)
This shows that warmth is necessary for germination.
Note that the seeds in the dark cuboard DID start to grow. This shows us that light is not needed for germination