Plants — Class 5 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 5 Science. How plants make new plants, how seeds travel, and how we grow our food.
1. Reproduction through flowers
The flower is the reproductive part of a plant. Making a new plant from it takes two steps, and they are not the same step.
Pollination is the transfer of pollen from the stamen, the male part, to the stigma, the female part.
Fertilisation is what happens afterwards, when the pollen and the ovule fuse inside the flower.
A useful way to hold them apart: pollination is the delivery, fertilisation is the joining. Delivery must happen first, but delivery alone produces nothing.
After fertilisation the ovary grows into a fruit and the ovules become seeds.
Pollen is carried by wind, water, insects and birds. A bee visiting a flower for nectar collects pollen on its body without meaning to, and leaves some at the next flower.
2. Vegetative propagation
Plants do not always need seeds. In vegetative propagation a new plant grows from a vegetative part — a stem, a root or a leaf — of the parent.
| Part used | How it works | Plants grown this way |
|---|---|---|
| Stem cutting | Cut a healthy stem just below a node, plant it in moist soil, and roots grow from the node | Sugarcane, rose, hibiscus, money plant |
| Root | A swollen root sprouts a new plant | Sweet potato, dahlia |
| Leaf | Baby plants grow on the leaf margins | Bryophyllum, the air plant |
This is completely natural. Many plants reproduce this way in the wild, and gardeners simply copy them. The new plant is an exact copy of the parent, which is why a grafted mango always gives the same fruit.
3. Seed dispersal
If every seed fell straight down under its parent, the seedlings would crowd together and compete for the same sunlight, water and nutrients. Most would die.
Dispersal scatters seeds so they can grow in new places.
| Carried by | Adaptation | Examples |
|---|---|---|
| Wind | Light seeds with wings or hair | Drumstick, cotton, dandelion |
| Water | Light, floating, waterproof | Coconut, lotus |
| Animals | Hooks that catch on fur, or tasty fruit eaten and passed out | Xanthium, tomato, guava |
| Explosion | The pod bursts and flings seeds out | Balsam, castor, pea |
A coconut is the clearest case. It is light for its size, sealed by a waterproof husk, and can float across the sea to sprout on a far shore.
4. Germination
A seed needs three things to sprout: water, air and a suitable temperature. Given these, the baby plant inside wakes, the root pushes down and the shoot pushes up.
Sunlight is not needed until the shoot breaks the surface, which is why a seed germinates in the dark under the soil.
5. From field to table: the steps of agriculture
| Step | What is done |
|---|---|
| Ploughing | Loosening and turning the soil, which helps air and water enter |
| Sowing | Placing seeds at the right depth and spacing |
| Adding manure or fertiliser | Supplying nutrients the soil lacks |
| Irrigation | Watering the field at the right times |
| Weeding | Removing unwanted plants that compete for water and nutrients |
| Harvesting | Cutting and gathering the mature crop |
| Storage | Keeping the grain dry and safe from pests |
Weeding matters more than it sounds. Weeds take the water, nutrients and sunlight meant for the crop, so leaving them cuts the yield.
6. Worked examples
Example 1. What is pollination?
Solution: The transfer of pollen from the stamen to the stigma of a flower.
Example 2. How does fertilisation differ from pollination?
Solution: Pollination is the transfer of pollen; fertilisation is the fusing of the pollen with the ovule afterwards.
Example 3. Name three plants grown from stem cuttings.
Solution: Sugarcane, rose and hibiscus.
Example 4. Which plant grows baby plants on its leaf margins?
Solution: Bryophyllum, the air plant.
Example 5. Why must seeds be dispersed?
Solution: So that they do not all compete with the parent and each other for the same sunlight, water and nutrients.
Example 6. How is a coconut adapted for dispersal by water?
Solution: It is light for its size and has a waterproof husk, so it floats across water and sprouts elsewhere.
Example 7. Name the three conditions a seed needs to germinate.
Solution: Water, air and a suitable temperature.
7. Practice
- Name the male and female parts of a flower involved in pollination.
- What happens to the ovary and the ovules after fertilisation?
- Name four agents of pollination.
- What is vegetative propagation?
- Give one plant each grown from a stem, a root and a leaf.
- Name the four methods of seed dispersal with one example each.
- Why does a seed not need sunlight to germinate?
- List the steps of agriculture in order.
- Why is weeding necessary?
8. Answers
- The stamen is the male part and the stigma the female part.
- The ovary becomes the fruit and the ovules become the seeds.
- Wind, water, insects and birds.
- Growing a new plant from a vegetative part of the parent, such as a stem, root or leaf.
- Stem: sugarcane. Root: sweet potato. Leaf: bryophyllum.
- Wind (drumstick), water (coconut), animals (xanthium), explosion (balsam).
- Because it germinates under the soil, using the food stored inside it until the shoot reaches the light.
- Ploughing, sowing, adding manure, irrigation, weeding, harvesting and storage.
- Because weeds compete with the crop for water, nutrients and sunlight, lowering the yield.
9. Summary
- Pollination is the transfer of pollen from stamen to stigma; fertilisation is their fusing afterwards.
- After fertilisation the ovary becomes the fruit and the ovules become seeds.
- Wind, water, insects and birds carry pollen.
- Vegetative propagation grows a new plant from a stem, root or leaf, and is entirely natural.
- Seeds are dispersed by wind, water, animals or explosion, so they do not crowd the parent.
- A coconut floats because it is light and waterproof.
- A seed germinates given water, air and a suitable temperature; sunlight comes later.
- Agriculture runs ploughing, sowing, manuring, irrigation, weeding, harvesting and storage.
- Weeds compete with the crop and lower the yield if left.
