Plant Reproduction

Bilingual Section. IES Aljanadic Natural Science. 2º ESO

REPRODUCTION, A CHARACERISTIC OF LIVING THINGS

1. Concepts of reproduction

Living beings are able to multiply and generate new individuals. The function of reproduction perpetuates life and maintains the species on the Earth.

The function of reproduction is not a question of increasing the numbers of beings of a species, but rather of replacing those which die.

At the same time, genetic information is transmitted from parents to children to develop and keep the being alive and to conserve the characteristics of the species in the future.

2. Types of reproduction: Asexual and sexual reproduction

There are basically two kinds of reproduction: asexual and sexual.

Asexual reproduction: a single individual is able to separate a part of its body and this develops into a new being. This happens in plants and some animals.

Sexual reproduction: two individuals of the opposite sex are necessary, a male and a female. Each one of them makes special cells, the gametes, which join together and become a single cell, a zygote, by means of fertilisation.

Animal fertilisation

Stages in sexual reproduction

In sexual reproduction there are three distinct phases.

1) Formation of gametes. One cell in a living thing divides and forms daughter cells, the gametes, which have half the number of chromosomes as their parent cell.

Animal gametes

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

2) Fertilisation is the fusion of the male and female gametes, which form a new cell, which is called the ovum (egg cell) or zygote.

3) Embryonic development is a long process in which the cells divide quickly and increase in number. The initial cell or zygote multiplies to make the embryo, and this becomes the new being.

3. ASEXUAL REPRODUCTION IN PLANTS

Plants which are produced asexually are identical to their progenitors. We call them clones.

Plants use different parts of their body to reproduce asexually. For instance:

Bulbs: bulbs are subterranean stems, formed by concentric meaty leaves. They have buds which will become a new plant, such as the case with an onion or tulip.

Stolons: are aerial stems which root when they touch the ground and produce new stems. If they become isolated from the mother plant they will become new individuals. An example of this is the strawberry.

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

Stem tubers: these are subterranean stems with a reserve of food and buds (often called ‘eyes´) which form roots and stems giving rise to new individuals, for example, the potato.

Rhizomes: rhizomes are subterranean stems which form new stems and shoots on certain stems to make a new plant. These can be found in canes, grass or ferns.

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

Human beings take advantage of the asexual reproduction of plants in agriculture to reproduce individuals rapidly. The techniques used are the following:

Cuttings: these are pieces of stem which are partially put into the ground and which become a new plant, such as roses and geraniums.

Shoots: this consists of burying a branch joined to the stem and waiting until it roots. Then it is cut off and it becomes a new plant, such as strawberries.

Grafts: this consists of introducing a branch of one species into the stem of another with fruit trees.

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

4. SEXUAL REPRODUCTION IN PLANTS

Plants also reproduce sexually using the gametes (sex cells), which are found in the flowers.

4.1 The structure of a flower

Typical flowers are made up of four concentric layers, or whorl, of modified leaves.

The whorls of the flower are as follows:

Calyx: this is made up of sepals, which are green. Their function is to protect the development of the flower.

Corolla: this is made up of brightly coloured petals. At the base of the petals there are glands which secrete sweet and fragrant substances like nectar. Their function is to attract insects to favour pollination.

Androecium: this is made up of stamen with a filament and some sacks known as anthers. Their function is the production of grains of pollen.

Gynoecium: this is also called the pistil. It is made up of one, two or three carpals. It is shaped like a bottle. The wide part is the ovary, the long part the style and, at the end, the stigma.

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

4.2 Pollination and fertilisation

Pollination is the transporting of the grain of pollen from the anther of the stamen to the stigma of the pistil. It can be done by the wind or insects such as bees or butterflies.

For fertilisation, the grain of pollen emits a pollen tube which allows the male gametes to reach the ovule, where the female gamete is (the oosphere).

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

4.3 Formation of seeds and fruits

Following fertilisation, the zygote produces the embryo which is inside the seed, the flower loses the calyx and the corolla and the ovary grows and becomes the fruit.

4.4 Seed germination

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Bilingual Section. IES Aljanadic Natural Science. 2º ESO

QUESTIONS ON PLANT REPRODUCTION

1) Make a list of the types of asexual reproduction in plants and find an example of each one.

a.

b.

c.

d.

2) Look for the meaning of the following words:

- stamen:

- petal:

- pistil:

- sepal:

- pollen:

- seed:

3) Can you explain the difference between pollination and fertilisation?

4) What is the purpose of the sepals and the calyx in flowers?

5) What are the male and female gametes called in plants?

6) How does a plant reproduce if it has got a rhizome?

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