Reproduction: How Life Continues
Chapter 11 — full, step-by-step solutions for every In-text prompt (Think It Over, Activities, Pause & Ponder, Threads of Curiosity) and the end-of-chapter “Revise, Reflect, Refine” exercise, with the chapter’s own diagrams.
In-Text — Think It Over & Activities
The reflective “Think It Over” prompts and the questions raised inside the chapter’s activities.
Asexual (vegetative) methods are preferred when the farmer wants to:
- Keep a prized variety exactly — clones are genetically identical, so fruit quality, taste and colour stay the same.
- Get faster results — cuttings/grafts flower and fruit earlier than seed-grown plants.
- Multiply plants with few or no viable seeds — e.g. banana, sugarcane, grapes, rose, potato.
Sexual methods (seeds) are preferred when the farmer wants:
- Variation to develop new/improved varieties (selective breeding, hybridisation).
- Disease resistance and adaptability across generations.
- Easy-to-store, easy-to-transport seeds for large-scale crops like wheat, rice, maize.
Complex organisms → sexual reproduction. It mixes genetic material from two parents (meiosis + fertilisation), creating variation. Variation lets a population adapt to changing environments, resist diseases and evolve — a big long-term advantage for long-lived organisms.
Simple organisms → asexual reproduction. Yeast and hydra are short-lived and often live in stable conditions where multiplying fast matters more than variation. Asexual reproduction is quick, needs only one parent, no mate and no gametes, so numbers can explode when conditions are good.
Yes — rounded outgrowths (buds) appear on the parent cells, and they do show the yeast is reproducing. In this process, called budding, a bud grows out from the parent, enlarges, and finally separates as a new, independent yeast cell.
For each pair you pick one of two beads, independently — so the total doubles with every pair.
Fruits form in every treatment where pollen could still reach the stigma (flowers/buds that kept their stamens, and the open uncovered flower). No fruit forms in the treatment where the stamens were removed and the flower was bagged — there was no pollen and the bag blocked any from outside.
| Strategy | Pollen / flower | Seeds formed |
|---|---|---|
| Wind (maize, wheat) | 5,00,000 – 10,00,000 | 50 – 200 |
| Insect (sunflower) | 20,000 – 40,000 | 800 – 1,000 |
(1) Pollen-to-seed ratio (rough mid-values):
Insect pollination is far more efficient per grain; wind pollination wastes most of its pollen.
(2) Why it still works: wind pollination relies on chance — most pollen never lands on a compatible stigma. By releasing millions of light grains, the plant raises the odds that enough reach a stigma, without spending on nectar, scent or bright petals.
In-Text — Pause & Ponder + Threads of Curiosity
Every “Pause and Ponder” question, plus the “Threads of Curiosity” prompt on sex determination.
The pollen tube carries the male gamete down through the style to the ovule. The next step is the male gamete fusing with the egg cell.
Both seeds are very light and carry fine, silky/feathery hairs (a tuft or “parachute”) that catch moving air, letting them float far from the parent plant.
Pollen travels from a flower on one plant to the stigma of a flower on another plant of the same kind.
In external fertilisation eggs and sperm are released into water, where fertilisation is left to chance. Many gametes never meet, and exposed eggs/young are swept away or eaten, so survival is very low. Producing thousands of eggs raises the chance some survive. In internal fertilisation, fertilisation is more certain and the embryo is protected inside the body, so few eggs suffice.
A growth spurt, broadening shoulders and a deepening (cracking) voice are secondary sexual characteristics in boys, caused by hormones as the reproductive organs mature.
- Next period = 28 days after the last onestart from 5 March.
- Days left in March after the 5th$31 – 5 = 26$ days.
- Remaining days fall into April$28 – 26 = 2$ → 2 April.
- Each gamete is haploidegg = 23, sperm = 23.
- Fertilisation adds them$23 + 23 = 46$.
Oral pills change hormones to stop ovulation, so they help prevent pregnancy — but they do nothing to block the contact and fluid exchange that spread infections.
Advantages:
- The long, protected childhood gives the large human brain time to develop.
- Lots of learning — language, social skills, problem-solving, tool use, culture passed from elders.
- Strong family and social bonds, improving survival and the success of the species.
Disadvantages:
- Heavy investment of parental time, energy and resources.
- Parents can usually raise fewer offspring at a time.
- The helpless infant is vulnerable and needs constant protection.
The mother always gives an X; the father gives either an X or a Y:
| Egg (mother) | Sperm (father) | Baby |
|---|---|---|
| X | X | XX → Girl |
| X | Y | XY → Boy |
Exercise — Revise, Reflect, Refine
Full solutions to all 13 end-of-chapter questions.
- Self-pollination
- Cross-pollination
- Fertilisation
- Tissue culture
Removing the anthers (emasculation) prevents the flower’s own pollen being used, and the pollen comes from another plant of the same species.
- Pollen germination on stigma
- Fertilisation
- Pollination
- Formation of zygote
- (iii) Pollinationpollen reaches the stigma.
- (i) Pollen germinationpollen tube grows down the style.
- (ii) Fertilisationmale gamete fuses with the egg.
- (iv) Zygote formationfertilised egg becomes the zygote.
Reason (R): The uterus wall is always prepared to receive the zygote.
- Both A and R true, R explains A.
- Both true, R does not explain A.
- A true, R false.
- A false, R true.
A is false: the zygote does not attach immediately — it undergoes several mitotic divisions while travelling down the oviduct over days, and only then implants.
R is false: the uterus lining is not always prepared — it thickens only after ovulation and is shed during menstruation if no fertilisation occurs.
Asexual reproduction involves a single parent and uses mitosis, which produces daughter cells with the same number and identical copies of chromosomes as the parent. With no fusion of gametes and no mixing of genetic material, offspring receive an exact copy of the parent’s genes.
The cycle prepares the uterus for pregnancy and sheds the lining if none occurs. When an embryo implants, the thick, blood-rich lining is needed to nourish it, so it is maintained — not shed. Pregnancy hormones also stop further ovulation and prevent the lining from breaking down.
Night flowers are pollinated by night-active pollinators (moths, bats). In the dark, bright colours are invisible, but white/pale flowers reflect faint moonlight and stand out, and they also rely on strong fragrance. Day flowers can use bright colours because bees, butterflies and birds see colours well in sunlight.
They are clones — genetically identical with no variation. If a disease can infect one plant, it can infect all of them the same way, so a single outbreak can destroy the whole crop. Sexually reproduced plants have variation, so some individuals may carry resistance and survive.
Self-pollination uses pollen and eggs from the same plant, so little new genetic material is mixed in. Over generations, offspring become more and more genetically similar and genetic diversity steadily falls.
Methods (asexual / vegetative): tissue culture (micropropagation), cuttings, grafting and layering.
- They use a single parent and mitosis, so each plant is an identical clone with the same desirable traits.
- They are faster than growing from seed.
- Tissue culture can produce thousands of healthy, disease-free plantlets quickly from a tiny piece of tissue (e.g. banana).
(i) Hypotheses:
- Sugar concentration affects the percentage/rate of pollen germination.
- There is an optimum sugar concentration where germination is maximum — too low or too high reduces it.
- In 0% (plain water) pollen germinates poorly or bursts.
(ii) Kept the same (controlled variables): same species and freshness of pollen, same number of pollen grains, same temperature, time, volume and pH of solution, same light/humidity, and the same microscope magnification — only the sugar % is varied.
- Tomato → Self-pollination. Stamens surround the stigma, so its own pollen falls on it.
- Wheat → Self-pollination. Pollination happens inside the flower before it opens.
- Papaya → Cross-pollination. Male and female flowers are on different trees, so pollen must travel between trees (by wind/insects).
| Place | Fruit set (%) | Fruit drop (%) |
|---|---|---|
| A — Natural pollination | ≈ 26% | ≈ 40% |
| B — With bee colony | ≈ 35% | ≈ 8% |
(i) Hypotheses: adding bee colonies increases pollination, raising fruit set and lowering fruit drop → higher yield (and the decline of natural pollinators lowers yield).
(ii) Parameters: independent = pollination method (natural vs bee colony); dependent = fruit set % and fruit drop %; controlled = apple variety, climate/season, orchard care, number of fruit-bearing branches.
(iii) Comparison: with bees, fruit set is higher (~35% vs ~26%) and fruit drop is much lower (~8% vs ~40%) — Place B gives a clearly higher effective yield.
The claim is not (always) correct. “Day 14” is only an average for an idealised 28-day cycle.
- Cycle length varies (commonly 21–35 days) and even month to month. Ovulation occurs about 14 days before the next period, not always 14 days after the last — so in a 30- or 35-day cycle it is later.
- Many factors — stress, illness, hormones, age, diet, irregular cycles around puberty — shift ovulation timing.
- So “always day 14” is an over-generalisation that fits only a perfect 28-day cycle.
How life continues…
From a single budding yeast cell to a developing human embryo — reproduction is nature’s way of passing life, and variation, to the next generation.