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4. VITAL FUNCTIONS

Talking book

In order to live, organisms use the function of nutrition to obtain the matter and energy they need.

They interact with their environment thanks to the function of interaction, and they continue to have descendants due to the function of reproduction.

4.1. Nutrition

Talking book

The purpose of nutrition is to ren

ew and help preserve the organism's structure as well as obtaining energy to perform the three vital functions.

Cellular metabolism is a combination of chemical reactions. This enables cells to obtain the necessary nutrients and energy to keep them alive.

In order to feed themselves, living things take substances from the environment which surrounds them, and cellular metabolism takes place in their cells.

Metabolism consists of two stages: anabolism and catabolism.

Cell metabolism

Anabolism

This process creates complex molecules using simple molecules.
It requires energy.

Catabolism

This process destroys complex molecules to create simple molecules.
It releases energy.

During cell metabolism, in addition to matter and energy, waste substances are released from the organism.

4.1.1. Nutrition types

Talking book

There are two types of nutrition, depending on the type of matter obtained:

Autotrophic nutrition: This type of nutrition is performed by organisms that obtain inorganic materials from the environment, which they transform into organic material. Plants, algae, and some bacteria perform autotrophic nutrition.
Heterotrophic nutrition: This is performed by organisms that take organic matter from the environment. Examples of living things that use heterotrophic nutrition are: animals, fungi, protozoa and some bacteria.

4.2. Interaction

Talking book

Interaction allows living things to interact with their environment, detect any changes in it and react to them.

Stimuli are the changes in the environment that may provoke a response in a living thing. They are perceived by the receptors, which are cells or structures specialised in perceiving stimuli.

Living things can respond to stimuli either with movements or by producing substances called hormones, which produce changes in how something functions or behaves.

4.3. Reproduction

Talking book

The purpose of reproduction is to create descendants and, in this way, continue the species.

There are two types of reproduction: asexual and sexual.

Asexual reproduction: a single individual creates multiple descendants which are identical. It occurs in all unicellular organisms and in some multicellular ones. Unicellular living things only have one cell, so they can only reproduce by using the same cell.

There are three main types:

Key concepts

In order to live, living things perform three vital functions: nutrition, interaction and reproduction.
Asexual reproduction results in the production of many offspring which are identical to the parent.
In sexual reproduction, two individuals are needed, and the offspring have characteristics from both parents.

• Bipartition: the cell divides into two cells of similar size.

• Budding: the cell also divides into two cells, but this time they are very different in size.

• Sporulation: one single individual divides its nucleus, creating many new individuals.

• Sexual reproduction: it requires two individuals of opposite sex. The number of descendants is smaller than in asexual reproduction and the offspring are not identical. Multicellular organisms perform this type of reproduction.

Some species are capable of performing both types of reproduction.

Activity 18
What is the purpose of nutrition?

Activity 19
What is the difference between the two types of nutrition? Relate each type of nutrition with its definition.

Activity 20
Our sense organs are receptors. What type is each one? There is more than one answer in one of them.

Activity 21
What type of asexual reproduction does each diagram show?

Activity 22
In this table, compare asexual and sexual reproduction.

	asexual reproduction	sexual reproduction
number of parents
number of offspring
genetic variability

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4. VITAL FUNCTIONS

4.1. Nutrition

4.1.1. Nutrition types

4.2. Interaction

4.3. Reproduction

Activity 18

Activity 19

Activity 20

Activity 21

Activity 22