Reproduction: How Life Continues

Fertilisation. The male gamete will travel through the pollen tube to fuse with the egg cell in the ovule.

Wind dispersal. They have hair-like structures (pappus) that help them float in air.

Cross-pollination (between different varieties of the same species).

External fertilisation has lower chances of fertilisation and survival due to environmental hazards (predators, water currents), so producing more eggs increases the probability of offspring survival.

Internal fertilisation, because gametes are protected inside the female’s body.

Condoms (male or female) are effective barriers that reduce the transmission of sexually transmitted infections (STIs).

Risk of STIs remains because pills only prevent pregnancy (by altering hormones), they do not block the transmission of infections.

Advantage: Extended dependence allows for prolonged learning, brain development, and social bonding, leading to higher intelligence and cultural transmission. Disadvantage: Requires significant parental investment, and survival of offspring is highly dependent on care.

(ii) Cross-pollination.

Correct order: (iii) Pollination → (i) Pollen germination → (ii) Fertilisation → (iv) Formation of zygote.

(iv) A is false, but R is true. Explanation: The zygote takes several days to travel and develop into a blastocyst before implantation; the uterus wall is prepared only after ovulation, not always.

Asexual reproduction involves only one parent and mitosis, which produces daughter cells with the same genetic material. There is no fusion of gametes or recombination.

During pregnancy, the embryo implants in the uterus and produces human chorionic gonadotropin (hCG) which maintains the corpus luteum. This prevents the breakdown of the uterine lining, so menstruation stops.

White or light-coloured flowers are more visible at night to nocturnal pollinators like moths and bats. They also often have strong fragrances to attract pollinators in the dark.

Vegetative propagation produces clones (genetically identical). If a disease affects one plant, all plants are equally susceptible. Sexually reproduced plants have genetic variation, increasing the chance that some individuals are resistant.

Genetic diversity would decrease drastically. Self-pollination leads to inbreeding and reduced heterozygosity, making the population less adaptable to environmental changes.

Vegetative propagation methods like cutting, grafting, layering, or tissue culture. These methods produce clones rapidly, maintaining desirable traits without the need for seeds or pollination.

(i) Hypothesis: Pollen germination rate depends on sugar concentration; optimal concentration exists for maximum germination. (ii) Controlled parameters: temperature, pollen source, time of observation, type of sugar, pH, and method of slide preparation.

Tomato – self-pollination; Wheat – self-pollination (cleistogamy); Papaya – cross-pollination (dioecious plant).

(i) Hypothesis: Beekeeping (managed pollination) increases fruit set and reduces fruit drop compared to relying on wild pollinators. (ii) Independent: pollination method; dependent: fruit set %, fruit drop %. (iii) Place B likely shows higher fruit set and lower fruit drop. (iv) Inference: Managed pollination improves apple yield; pollinator decline can be mitigated by beekeeping.

The claim is false. (i) Menstrual cycle length varies (21–35 days) among individuals; ovulation occurs about 14 days before the next period, not necessarily on day 14. (ii) Cycle length can vary due to stress, illness, or hormonal changes, shifting ovulation day.

(i) Wind-pollinated: ratio ≈ 5,000–10,000:1; insect-pollinated: ratio ≈ 20–50:1. Wind pollination is inefficient (most pollen wasted), so more pollen is needed. (ii) Wind-pollinated plants produce enormous pollen because wind dispersal is random; high numbers increase the chance that some pollen lands on a compatible stigma.

Pollination (transfer of pollen to stigma) is necessary. Flowers without stamens (removed) did not form fruits unless pollen was artificially transferred.