Life Cycle of Plants

Basic Parts of a Plant

There are thousands of different types of flowering plants, but they all have the same basic parts:-

1. Roots - Anchors the plant into the soil, takes in water and nutrients from the soil.

2. Stem - Main support column of the plant, grows as tall as possible to get as much sunlight as possible.

3. Leaf - Big and wide to receive as much sunlight as possible. Contain the chemical Chlorophyll to absorb light energy for Photosynthesis.

4. Flower - The reproductive part of the plant. Is sometimes brightly coloured to attract insects.

The Life Cycle of a Plant

The diagram below shows the stages of a plant's life cycle:-

The life cycle above shows the stage of growth for a plant, from seed to flowering plant to the production of more seeds. 

We could start the story of a plant at any point in this cycle, but for now we will start with a flowering plant and follow the whole process. 

Flowers 

Flowers may look very pretty, and are most of the reason that we have them in our  homes, but the flowers serve a really important role to the plant; they are the plant's reproductive system. 

When a living thing makes a new individual like itself, this is called reproduction. To reproduce, most organisms produce special sex cells called Gametes. 

1. In an animal, the male gamete is the sperm cell and the female gamete is the egg cell.

2. In a plant, the male gamete is Pollen and the female gamete is the Ovule. 

To reproduce, the male sex cell must meet and join with the female sex cell. 

Parts of a Flower

Flowers come in thousands of different colours shapes and sizes, but all flowers have the same basic structure:-

Parts of a flower and their function:-

1. Sepal - Green cover that protects the flower as it develops.

2. Petal - Brightly coloured to attract Insects for pollination.

3. Stamen and Anther  - The "male" part of the plant; the stamen supports the anther, where the pollen is produced.

4. Stigma, Style and Ovary - The "female" part of the plant; the sticky stigma collects pollen, which passes down the style to the ovary, where fertilisation takes place. 

Pollination

The parts of a flower shown above all work together as the plant's reproductive system. However, the plant cannot just reproduce on its own, they need help.

Plants can be pollinated by two methods:-

1. Wind Pollination - The pollen is light enough for the wind to blow the pollen onto other flowers.

2. Insect Pollination - The pollen is sticky, insects (or other animals) feeding on the nectar in the flower carry the pollen from one flower to another. 

Wind Pollination

Wind Pollination is the process of pollen being transferred between plants by the wind. In order to get blown long distances, the pollen must be very light. This makes the pollen very small and fine, which can be carried by the smallest of breezes. As the wind can blow the pollen anywhere, it only has a small chance of landing on the right plant, so wind pollinated flowers produce large amounts of pollen. 

This large amount of pollen in the air can cause health problems for certain people. It is this wind blown pollen that causes Hay Fever. 

Plants that are pollinated by the wind include:-

1. Wheat

2. Rice

3. Barley

4. Oak Trees

5. Chestnut Trees

6. Pine Trees

7. Willow Trees

Insect Pollination

Insect Pollination is the process of pollen being transferred between plants by insects or other animals (such as birds or bats). In order to get carried by an insect, the pollen must be very sticky.

Fertilisation

Pollination occurs when pollen from the anther of a flower was transferred to the stigma of another flower.  Once the pollen reaches the stigma, the process of fertilisation can begin:

Once fertilisation has occurred, the flower changes completely. The ovary swells in size to form a fruit and the fertilised ovule becomes a seed.

The diagram below shows the main parts of a plant seed:-

A seed has to contain everything a new plant needs to start growing. It contains the young plant (embryo) and a store of food. This is surrounded by a tough, protective coat.

Seed Dispersal 

Seeds can be dispersed (spread) through a range of methods : 

Germination 

Once the seed has been dispersed, the process of germination can begin. Sometimes this can happen straight away or the seed can remain dormant for months or years before germinating.

The process of germination is the growth from a seed into a seedling (a small plant) . Germination can only start when the seed experiences the right conditions for growth. How much water and oxygen is available and what the temperature is, control when germination happens. 

The diagram below shows the stages of germination, from a seed to a seedling:-

The videos below show time-lapse footage of plant growth :