NATURAL SCIENCE. UNIT 4:  ANIMALS AND PLANTS

The vital functions in animals

There are three vital functions: nutrition, interaction and reproduction.

● The nutrition function

* Animals eat and digest food.

* Animals breathe by using oxygen from water or air.

* By combining oxygen and the substances from food, animals obtain energy to live and make other substances to grow.

* Animals excrete waste products from their bodies, through sweat, urine, faeces, etc.

● The interaction function

They all have parts of their bodies which help them detect and react to changes.

Most animals have: sense organs, a nervous system and a locomotor system.

● The reproduction function

Reproduction in animals is sexual because it involves two different sexes: the male and the female.

Most animals are unisexual, only one sex:

* Male: they produce sperm.

* Female: they produce ovules.

Some animals, like snails, have two sexes. They are hermaphrodites.

The stages in animal reproduction are:

* Fertilization: it is the union of an ovule and a sperm. The result of the union is called zygote. The embryo grows from the zygote.

* The development of the embryo: in viviparous animals the embryo grows in the mother’s womb. It is called gestation. In oviparous animals the embryo grows inside an egg. It is called incubation.

* Birth: Oviparous animals hatch from eggs. Viviparous animals are born from their mother’s womb.

Plants: nutrition and interaction

● The nutrition function

* Plants absorb water and minerals and these rise to the leaves. Leaves absorb carbon dioxide.

In the leaves, plants make photosynthesis. They use The Sun’s energy, the water and carbon dioxide to make their own food.

* Like animals, plants take oxygen. They combine the food with oxygen to obtain energy and to create substances to grow.

* Plants excrete waste products from their bodies. For example, they excrete oxygen.

● The interaction function

Plants do not have sense organs, a nervous system or a locomotor system.

Despite this, plants react to changes in light, temperature, humidity, etc.

● The parts of a plant and their functions

* The roots grow downwards. They have small hairs that absorb water and minerals. The water and minerals rise up the plant.

* Leaves and photosynthesis. Leaves are generally flat and green. Photosynthesis takes places in the leaves:

- The leaves receive the mixture of water and minerals.

- The leaves absorb carbon dioxide from the air.

- Using The Sun’s energy, water and minerals combined with carbon dioxide and form the substances which are the plant’s food, a liquid called sap.

* The stem and the circulation of sap. The stem grows upwards and supports the branches and leaves. The substances the plant needs circulate through the stem:

- Water and minerals move from the roots to leaves.

- Sap moves from the leaves to other parts of the plant.

Plants: reproduction

● Sexual reproduction

The reproduction of plants is sexual because there are both male and female reproductive organs.

Most plants have reproductive organs in their flowers:

- The stamens are the male organs of the flower. They produce grains of pollen.

- The pistil is the female organ of the flower. It produces and contains ovules.

Most plants have flowers with both stamens and pistil. Some plants have male flowers (with stamens) and female flowers (with pistil).

In most flowers, the stamen and pistil are surrounded by special leaves: the petals of the corolla and the sepals of the calyx.

● The reproduction function in plants

There are different stages:

* Pollination. Wind or insects carry the pollen from the stamen of one plant to the pistils of another.

The union of a grain of pollen and the ovule of the pistil is fertilization.

* The formation of the seed and fruit. The fertilized ovule becomes the seed. The pistil grows and becomes the fruit.

The seeds are usually inside the fruit. Fruit can be hard, like walnut, or soft, like an orange, an apple.

* Dispersal of seeds and germination. Some fruits open to disperse their seeds. Others are eaten by animals, which excrete the seeds with their faeces.

When a seed lands in soil with the right conditions it germinates: a new plant grows (the embryo grows with roots and a stem with leaves). At first it feeds on substances in the seed and then it begins to make its own food.