Reproduction in Plants and Animals Questions

About Reproduction in Plants and Animals

Medium ~110 min study

Reproduction is the one process a living thing can do without and still survive, yet no species can do without it. That is what makes the chapter unusual. Every other function keeps an individual alive; this one keeps the species going. The chapter takes that single idea and follows it through organisms as different as bacteria, flowering plants and human beings, which is why it covers so much ground.

The material splits cleanly in two. First comes reproduction without gametes, where a parent divides, buds or regenerates and the offspring are identical to it. Then comes sexual reproduction, where two haploid gametes fuse and the offspring differ from both parents. Plants are treated first, through the structure of the flower, the transfer of pollen and the fertilization that follows. The human system comes last, with the organs, the gametes they make, the cycle that prepares for pregnancy, and the development that follows fertilization.

For the examination the difficulty is rarely the concept and almost always the vocabulary. Terms arrive in near identical pairs, such as syngamy and triple fusion, Sertoli and Leydig cells, implantation and parturition. Questions are built precisely on those pairs, so the surest preparation is to be able to separate each pair in one sentence.

What you'll learn

• Distinguish asexual from sexual reproduction and give examples of each.
• Describe fission, budding, fragmentation and regeneration with the organisms that show them.
• Identify the four whorls of a flower and say which are essential and why.
• Compare self pollination with cross pollination and relate floral structure to the pollinating agent.
• Explain double fertilization and trace what the ovary and ovules become afterwards.
• Label the parts of the human reproductive system and state the function of each.
• Outline the sequence from fertilization through implantation and gestation to parturition.
• Name the common contraceptive methods and classify them by how they work.

Before you start

• The structure of a plant cell and an animal cell from earlier classes.
• An understanding of mitosis and meiosis and why gametes are haploid.
• Basic familiarity with the flower as the reproductive part of a plant.

Reproduction in Plants and Animals explained

What this chapter covers

Vegetative reproduction

New plants arise from a vegetative part of the parent, with no gametes involved. Underground stems such as ginger carry buds that grow into fresh plants, and Bryophyllum produces adventitious buds along the notched margins of its leaves. Because only one parent is involved, the offspring are genetically identical to it.

Asexual reproduction

Several distinct modes appear here. In fission a parent cell simply divides into two or more daughter cells, which is how many bacteria and protozoa multiply. In budding a small outgrowth forms, enlarges and separates, as in yeast. Fragmentation and regeneration allow broken pieces to grow into complete individuals, which Hydra demonstrates.

Sexual reproduction in plants

The flower is the reproductive structure. Calyx and corolla form the accessory whorls that protect and attract, while androecium and gynoecium form the essential whorls that actually produce gametes. The ovule, held within the ovary, contains the embryo sac in which fertilization later takes place.

Pollination and its agents

Pollination is the transfer of pollen from anther to stigma. When it reaches the same flower it is self pollination; when it reaches a different one it is cross pollination. Each agent leaves a mark on floral structure: wind pollinated flowers carry large feathery stigmas to intercept drifting pollen, while insect pollinated flowers are coloured, scented and offer nectar.

Fertilization in plants

The pollen grain germinates and its vegetative cell forms a pollen tube, while its generative cell divides to give two male gametes. One fuses with the egg in syngamy to form the zygote; the other fuses with the polar nuclei to form the endosperm. Because two fusions occur, the event is called double fertilization. Afterwards the ovary becomes the fruit and the ovules become the seeds.

The human reproductive system

Sperms are produced in the seminiferous tubules of the testes, where Sertoli cells nourish them and Leydig cells outside the tubules secrete testosterone. The sperms then pass to the epididymis, a long coiled tube in which they are stored and mature. In the female the ovaries produce ova, and the Graafian follicle secretes estrogen while the corpus luteum secretes progesterone.

Menstrual cycle, pregnancy and contraception

The menstrual cycle is the rhythmic set of events running through a woman's reproductive life. If fertilization occurs, the blastocyst attaches to the uterine lining in implantation, and the placenta forms as a temporary association supplying the embryo. Parturition is the expulsion of the young one at the end of gestation. Contraceptive methods, including intrauterine devices, hormonal pills and barriers, prevent unwanted pregnancy.

Common mistakes to avoid

• Confusing syngamy with triple fusion. Syngamy gives the zygote; triple fusion gives the endosperm, and together they are double fertilization.
• Swapping Sertoli and Leydig cells. Sertoli cells nourish developing sperms inside the tubules; Leydig cells lie outside and secrete testosterone.
• Naming the calyx and corolla as essential parts. They are accessory; the androecium and gynoecium produce the gametes.
• Assuming sperms are produced in the epididymis. They are produced in the seminiferous tubules and only stored and matured in the epididymis.
• Attributing estrogen to the corpus luteum. The Graafian follicle secretes estrogen, while the corpus luteum secretes progesterone.

Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.

Frequently asked questions

What is the difference between asexual and sexual reproduction?

Asexual reproduction needs one parent and no gametes, so the offspring are genetically identical to that parent. Sexual reproduction involves the fusion of two haploid gametes from two parents, so the offspring carry a mixture of characters and differ from both. Fission and budding are asexual; flowering and human reproduction are sexual.

What is double fertilization in plants?

In angiosperms the pollen tube delivers two male gametes into the embryo sac. One fuses with the egg cell to form the diploid zygote, an event called syngamy. The other fuses with the polar nuclei to form the endosperm, called triple fusion. Because two fusions occur together, the process is named double fertilization.

Which parts of a flower are called essential?

The androecium and the gynoecium are the essential whorls, because they produce the male and female gametes respectively. The calyx and the corolla are accessory whorls: the calyx protects the flower while it is still a bud, and the corolla attracts pollinating agents with colour and scent.

Why do wind pollinated flowers have feathery stigmas?

Wind pollination scatters pollen without any direction, so very little of it reaches a stigma by chance. A large feathery stigma presents a wide, branching surface that intercepts far more drifting grains. Such flowers usually lack bright colour, scent and nectar, since none of those would attract the wind.

What is the function of the epididymis?

The epididymis is a single highly coiled tube attached to the testis. Sperms formed in the seminiferous tubules pass into it, and there they are stored, become concentrated and complete their maturation. Only after this maturation are the sperms able to fertilize an ovum.

What is implantation?

Implantation is the attachment of the blastocyst to the endometrium, the inner lining of the uterine wall. It follows fertilization and the early divisions of the zygote. Once attached, the embryo can draw nourishment from the mother, and the placenta develops as the connection between the two.

What is the placenta and what does it do?

The placenta is a temporary association formed between the developing embryo and the maternal tissues after implantation. It allows oxygen and nutrients to pass from the mother to the embryo and waste products to pass in the opposite direction. It is discarded after the birth of the child.

What are contraceptive devices?

Contraceptive devices are the methods and devices used to prevent unwanted pregnancy, and contraception is regarded as one of the main birth control measures. They work in different ways: an intrauterine device such as Copper T is placed in the uterus, oral pills act through hormones, and a diaphragm acts as a barrier.