Reproduction

The governing concept is chemotropism, in which growth is directed by chemical substances. During reproduction in flowering plants, chemical signals associated with the ovule and female tissues guide the pollen tube through the style toward the ovule, allowing the male gametes to reach the embryo sac. Light, gravity and touch are not the primary directional cues in this case. Therefore option B is correct, and the item also connects directly with plant reproduction.

The correct answer is A. Reproduction produces offspring that can replace individuals as they die, allowing the species to continue across generations. It is not essential for the immediate survival of an individual organism.

The correct answer is B. Asexual reproduction involves one parent, so offspring inherit their genetic information from that parent and are usually very similar to it. Small DNA-copying changes can still cause differences.

The correct answer is C. In sexual reproduction, gametes from two parents combine, bringing together genetic information from both. This creates new combinations of traits in offspring and generally increases variation.

The correct answer is D. A copying error can change genetic information and introduce a difference in an offspring, creating variation. Its effects can vary; a change is not necessarily harmful or beneficial.

The correct answer is A. In binary fission, one parent cell divides to form two daughter cells. In multiple fission, it can divide to produce many daughter cells. Both are forms of asexual reproduction.

The correct answer is A. Amoeba has an irregular shape and no fixed body axis, so its binary fission can occur in different planes rather than in one definite plane.

The correct answer is A. Leishmania has a definite body orientation associated with its flagellum, so its binary fission occurs in a specific plane, typically along its length.

The correct answer is A. Rhizopus spores have protective walls that help them survive unfavourable conditions. When conditions become favourable, they can germinate and grow into new organisms.

The correct answer is A. In Hydra, a small bud grows as an outgrowth on the parent’s body and can develop into a new Hydra. This is a form of asexual reproduction involving one parent.

The correct answer is A. In fragmentation, the organism breaks into pieces and a piece can grow into a new organism. Regeneration is the regrowth of lost parts; in some simple organisms, a fragment can regenerate a whole body. The two processes are related but not identical.

The correct answer is A. Planaria has special cells that can divide and differentiate into different cell types. This enables a body fragment to rebuild the missing tissues and, under suitable conditions, form a complete organism.

Vegetative propagation produces new plants from parts of a parent plant. The new plants usually retain the parent’s useful traits, so farmers can multiply them quickly and uniformly.

A stem cutting is a part of the parent plant that can grow into a new plant. Since this happens without seed formation or fertilisation, it is vegetative propagation.

Tissue culture uses cells or tissue from a parent plant to grow new plants. Because they come from the same source and are produced asexually, the plants are generally very similar to the parent and to one another.

Pollination brings pollen to the stigma. The pollen grain can then germinate and form a pollen tube, which carries the male gametes towards the ovule for fertilisation.

Self-pollination uses pollen from the same flower or another flower on the same plant, so it usually introduces less variation. Cross-pollination between plants of the same species can combine different inherited traits and may increase variation.

After a pollen grain germinates on the stigma, it forms a pollen tube. The tube grows towards the ovule and carries the male gametes for fertilisation.

After fertilisation, the ovule develops into a seed, while the ovary usually develops into a fruit. The embryo forms within the developing seed.

Water helps activate a seed, but germination also requires oxygen from the air for respiration and a suitable temperature for the processes of growth.

The testes produce sperm cells and secrete male sex hormones, including testosterone. Testosterone contributes to the development of male reproductive functions and secondary sexual characteristics.

The scrotum keeps the testes at a temperature slightly below the body’s internal temperature. This cooler temperature supports normal sperm production.

The sperm duct carries sperm from the epididymis towards the urethra, along the route by which sperm leave the male reproductive system.

Ovaries produce egg cells and female sex hormones. These hormones help regulate reproductive functions and body changes during puberty.

After release from the ovary, the egg enters a fallopian tube. Sperm can travel there, so fertilisation usually takes place in the tube.