UNIT 8. FUNCTIONS OF LIVING THINGS

THE NUTRITION

1. CHARACTERISTICS OF LIVING THINGS

All living things have the following characteristics:* They all consist of cells.* They all have the same biomolecules: carbohydrates, lipids, proteins, etc.* They all perform three vital functions: nutrition, interaction and reproduction.

2. WHAT ARE CELLS?

Cells are the structural and functional units of all living things. Cells are usually microscopic sizes, so you must use microscopes to be able to see them, although some may be seen with the naked eye, e.g. hen's eggs.

Cells have three basic structures:

The cell membrane is the thin layer which separates the inside of the cell from its surrounding environment.

Cytoplasm is the gelatinous, semi-transparent fluid which fills most cells. It contains structures called organelles, which are responsible for cell functions.

The nucleus carries the genetic information of living things which passes from one generation to the next. Genetic material can refer to anything from a small fragment of DNA (gen) or the entire genome. A genome is the complete set of genes, in other words, the chemical units of hereditary information carried by a cell.

The most important plasma organelles are:

Rough Endoplasmic Reticulum (RER): stores and transports proteins.

Ribosomes: make proteins.

Smooth Endoplasmic Reticulum (SER): transports lipids.

Vacuoles: store substances.

Mitochondria: responsible for cell respiration.

Chloroplast: where photosynthesis takes place.

Golgi body: where substances produced in the ER are processed.

3. TYPES OF CELLS

Depending on complexity, cells can be classified as:

PROKARYOTIC CELLS

EUKARYOTIC CELLS

Are smallAre large

Dont have a nucleus, the DNA is floating in the cytoplasm.Have a nucleus and the DNA is inside the nucleus.

Only have ribosomesHave all cytoplasmic organelles

Have cell wall and membrane Only have cell membrane

Are only bacteria Are animals, plants, mushrooms, algae

Depending of its type of nutrition, cells can be classified as:

ANIMAL CELLPLANT CELL

Have mitochondria to do the cell respiration.Have chloroplasts to do the photosynthesis, and mitochondria for the cell respiration.

The nucleus is in the centre.The nucleus is displaced.

Has a rounded form.Has a polyhedral form.

Have much small vacuoles.Have few large vacuoles.

4. THE NUTRITION FUNCTION

Nutrition is the set of process used to obtain energy with which the cell performs the vital functions or replaces tissues. But depending on how it is processed, there are two types of nutrition.

a) AUTOTROPHIC NUTRITION

This nutrition is performed by plants, algae and cyanobacteria. These living things make its own energy, with a chemical reaction called Photosynthesis. For them, its necessary that:

Root absorbs water and mineral salts.

Leaves absorb carbon dioxide (CO2) and the suns energy.

As a result, it obtains glucose and releases oxygen (O2).

ENERGY OF SUN

H2O + CO2 C6H12O6 + O2

WATER CARBON DIOXIDE GLUCOSE OXIGEN MOLECULAR

For this reason, it is necessary that the photosynthesis process is performed during the day.

b) HETEROTROPHIC NUTRITION

This nutrition is performed by animals, mushrooms, most bacteria and Protoctista. These living things cannot make its own energy, for this reason, caught the energy from the surrounding environment. This occurs when a lion eats a gazelle, or when a mushroom feeds on horse faeces, or when a bacterium decomposes a body.

5. CELL RESPIRATION

When a living thing (autotrophic or heterotrophic) obtains organic matter (glucose), it is burned in the presence of oxygen to obtain energy. This way of obtaining energy is more useful and the living thing obtains a lot of energy. Reactions which allow them to obtain this energy are called Cell Respiration, and the chemical reaction is:

C6H12O6 + O2 H2O + CO2 + ENERGY

But there is a group of living things, that doesnt use cell respiration to obtain energy. They use another reaction called FERMENTATION, and without oxygen, they obtain less energy with glucose, and obtain lactic acid and ethanol. These chemical reactions are used in the manufacturing of wine or yoghurt.

6. WHY IS PHOTOSYNTHESIS IMPORTANT?

Most living things obtain energy by burning the organic matter in the presence of oxygen. For this reason, oxygen is essential. The only living things capable of releasing oxygen into the atmosphere are the photo-synthetic beings (plants, algae and cyanobacteria), the rest take in oxygen which is produced by plants in order to cell respiration.

7. HOW IS NUTRITION PRODUCED IN THE UPPER ANIMALS?

The upper animals do nutrition thanks to four apparatus: digestive, respiratory, circulatory and excretory systems.

The digestive system obtains the food nutrients with digestion and absorption.

The respiratory system obtains oxygen and ejects carbon dioxide.

The circulatory system transports oxygen and nutrients to cells and collects carbon dioxide and waste substances.

The excretory system ejects the waste substances, such as urea and uric acid.