Sexual reproduction：练习题

Which part of an insect-pollinated flower is responsible for producing pollen?

The diagram represents the structure of two different pollen grains, labelled 1 and 2. Pollen grain 1 is small, light, and has a smooth surface. Pollen grain 2 is large, heavy, and covered in sticky hooks.

Which statement correctly identifies the pollination method for these grains?

What is the primary role of the pollen tube after a pollen grain has landed on a compatible stigma?

Which statement correctly describes the process of sexual reproduction?

A species of plant can reproduce both sexually and asexually. Under which environmental conditions would sexual reproduction be more advantageous to the survival of the population?

What is meant by fertilisation?

Compare the male gamete (sperm) and female gamete (egg cell) in humans based on their size and motility.

Explain the importance of gametes having a haploid nucleus in the context of sexual reproduction.

Reproduction is essential for the survival of a species. Some organisms can reproduce both sexually and asexually.
(a) Describe the fusion of nuclei during sexual reproduction and state the change in ploidy that occurs.
(b) Discuss why sexual reproduction might be more advantageous than asexual reproduction for a population of animals living in an environment where a new predator has been introduced.

Following fertilisation in humans, the development of the offspring involves several complex stages and the formation of supporting structures.

(a) Describe the sequence of events that occurs from the formation of the zygote to its implantation in the uterus.
(b) Explain how the placenta is adapted to facilitate the efficient exchange of dissolved nutrients and gases between the mother and the fetus.
(c) The placenta is often described as a barrier; however, it is not a complete barrier. Explain why some substances, such as toxins or certain pathogens, can still affect the fetus and provide one specific example of such a substance.