Secrets of Reproduction and Heredity
FoundationFlowering plants make fruit and seeds through pollination and fertilisation; roots, stems and leaves can also grow new plants. Offspring inherit traits like skin colour and tongue rolling, but acquired traits like hair length are not passed on.
- Flowering plants make fruit and seeds through pollination and fertilisation.
- Roots, stems and leaves all reproduce: sweet potato by root, onion by stem, echeveria by leaf.
- Plants raise chances with many seeds; mammals by caring for their young.
文體小知識：說明文把複雜的過程一步一步講清楚。這一篇帶你看看植物怎樣傳宗接代，再查查你和家人有什麼相似之處。
§Text Passage
1Flowers open and fade; it looks ordinary, yet it is the vital process of plant reproduction. A complete flower has petals, sepals, stamens and a pistil. The stamens make pollen; inside the pistil are ovules. When a mature flower opens, it is ready for the great task of continuing its kind.
2Pollen must travel from the stamen to the stigma of the pistil; this is pollination. Bees and butterflies, sipping nectar, get covered in pollen and carry it to another flower — insect pollination. Wind also blows light pollen elsewhere — wind pollination. When pollen reaches the stigma and joins with an ovule, fertilisation happens. After it, the ovary slowly swells into fruit and the ovules become seeds.
3Some plants can reproduce without seeds. The roots of radishes and sweet potatoes are full of food; plant a root and a new plant grows. Onions and garlic are actually special stems; buried in soil, they sprout leaves. Lay leaves of echeveria or air plant on damp soil and tiny plantlets appear on the leaf edges. Growing from roots, stems and leaves is a great power of plants.
4Living things all work to raise the number and survival of their young. One flower can make thousands of seeds; even if most are eaten or land in poor places, as long as a few sprout, the kind lives on. Mammals such as cats and dogs have few young each litter, but the mother feeds and cares for the cubs and teaches them to find food, so far more of the young survive.
5Why do children look like their parents? Because offspring inherit traits from them: skin colour, eye colour and the shape of the earlobes; whether you can roll your tongue or bend your thumb far back is also inherited. But acquired traits such as hair length or the skill of riding a bicycle are not passed to the next generation. Do a small survey and compare with your family — the secrets of heredity hide in daily life.
1Summary 重點摘要
Flowering plants make fruit and seeds through pollination and fertilisation; roots, stems and leaves can also grow new plants. Offspring inherit traits like skin colour and tongue rolling, but acquired traits like hair length are not passed on.
2Vocabulary cards Vocabulary
The process by which living things produce young and continue their kind.
The carrying of pollen from the stamen to the stigma.
The joining of pollen with an ovule, after which fruit and seeds form.
Seeds carried far away by wind, water or animals to sprout and grow.
Growing new plants from food-storing roots or stems, such as sweet potatoes and onions.
A body feature passed from parents to children, such as eye colour.
A feature formed after birth, such as hair length; it is not inherited.
The next generation produced by living things.
Animals that feed their young with milk, such as cats, dogs and whales.
The ability to curl the tongue into a tube; a common example of an inherited trait.
3Step by step Steps
- Step 1: Know the parts of a flowerTake a complete flower and observe it carefully. From outside in, there are the sepals that protect the bud, the bright petals that attract insects, the stamens topped with pollen, and the pistil in the centre. The anthers of the stamens hold countless tiny pollen grains with male reproductive cells; the sticky stigma of the pistil catches pollen, and the ovary at its base holds ovules. With both male and female parts, plus the protection and invitation of petals and sepals, a flower is really a finely designed reproduction factory.
- Step 2: Pollination and fertilisationPollen travelling from anther to stigma is called pollination. Insect-pollinated flowers are bright, sweet and fragrant, inviting bees and butterflies to help; wind-pollinated flowers like maize make light pollen in huge amounts for the wind to carry. After landing on the stigma, the pollen grows a fine tube down into the ovary and joins with an ovule — fertilisation. When it succeeds, the petals usually wither; the ovary keeps growing into fruit and the ovules become seeds. The flesh of an apple grew from the ovary, and the brown pips in the middle are the seeds.
- Step 3: Seed dispersal raises chancesAfter seeds ripen, plants must send them far away. Dandelion seeds wear a crown of hairs and drift like little parachutes; coconuts float across the sea to distant islands; the fruits of cleavers have hooks that cling to animal fur for a free ride; ripe bean pods twist open and shoot the seeds out. Scattered far and in great numbers, seeds do not crowd one spot fighting for light and water, nor are they all wiped out by one accident, so the chance that the kind carries on rises greatly.
- Step 4: Roots, stems and leaves can reproduceNot every plant needs seeds. Radishes and sweet potatoes reproduce with roots full of stored food; plant a root piece and new shoots appear. Onions, garlic and potatoes are really special food-storing stems; buried in soil, they send out stems and leaves from their buds. Echeveria and air plants reproduce with leaves: lay a leaf flat on damp soil and tiny new plants grow from its edges and base. Plants grown this way are exactly like the parent, which is why gardeners often use it to multiply flowers.
- Step 5: Ways to raise the young's chancesLiving things use different tricks to raise the number and survival of their offspring. Plants win by numbers: one flower makes thousands of seeds, and surely a few land somewhere suitable to root and sprout. Mammals win by care: a mother cat has only a few kittens a litter, but she feeds, grooms and teaches them to hunt until they can live on their own; a kangaroo carries her joey in her pouch. Birds build nests, hatch eggs and feed the chicks. Different strategies, one goal — helping the next generation grow up safely.
- Step 6: What inherited traits areChildren always look somewhat like their parents because some features pass from parent to child: these are inherited traits. Common examples are skin colour, eye colour, straight or curly hair, and whether the earlobes hang free or are attached. Two more fun examples: some people can curl their tongue into a tube and some cannot; some can bend the thumb far back and others only a little. All these come from heredity. Try a small class survey and see how many classmates can roll their tongues or bend their thumbs.
- Step 7: Telling inherited from acquired traitsNot every trait is inherited. The test is simple: features fixed by parents at birth that do not change with personal experience are inherited; those changed after birth by environment, practice or habits are acquired. Cut hair grows again — its length is not inherited. Knowing how to swim, speaking Putonghua, scars on the skin: all acquired after birth, none passed to children. Skin colour, blood type and earlobe shape come with birth. Knowing the difference, you will not believe a son swims naturally just because his father does.
5Worked example Example
Example: The class looks at a family photo. The father has free earlobes, can roll his tongue and has darker skin; the mother has free earlobes, cannot roll her tongue and has lighter skin; the son has free earlobes, can roll his tongue and has darker skin — and he wears glasses and keeps his hair short. Which traits in the photo are inherited? Which are not?
- The son's earlobes match his parents' — all free earlobes; earlobe shape is an inherited trait.
- The son rolls his tongue like his father, and his darker skin resembles his father's too; both can be inherited.
- The glasses are worn because of eyesight, and the short hair is the result of a haircut; both formed after birth.
- Conclusion: inherited traits come from parents and exist from birth; acquired traits arise from life experiences and are not inherited.
- Answer: Free earlobes, tongue rolling and skin colour are inherited traits, fixed by the parents at birth. Glasses and short hair are acquired traits with nothing to do with heredity.
6Common mistakes Mistakes
7Quick check Quick check
Q1What is the carrying of pollen from stamen to stigma called?
Q2What does the ovary become after fertilisation?
Q3Which organ does echeveria use to reproduce?
Q4Give one example of an inherited trait.
Q5Is hair length inherited?
8Recap Recap
- Flowering plants make fruit and seeds through pollination and fertilisation.
- Roots, stems and leaves all reproduce: sweet potato by root, onion by stem, echeveria by leaf.
- Plants raise chances with many seeds; mammals by caring for their young.
- Skin colour, tongue rolling and earlobe shape are inherited traits.
- Acquired traits such as hair length are not passed to the next generation.