How are we able to support so many organic processes at the same time? As we need to carry out many life processes at the same time, our organism is arranged into organ systems. There are different types of systems:
Takes in, breaks down and absorbs the soluble products in
food and removes undigested food. This is the way all nutrients and energy enter the body.
This consists of the organs associated with breathing and gas exchange. The breathing system helps supply oxygen for respiration and removes carbon dioxide, e.g. lungs in mammals, gills in fish. The leaves of plants have the same function.
This transports all soluble materials around the body. The heart pumps the blood which circulates in blood vessels. Plants move water and dissolved chemicals through vascular bundles (veins) in the stem, leaves and roots.
Wastes produced by the cells are removed from the body. Excretion usually refers to the removal of urine by the kidneys but should also include the lungs and skin as organs that get rid of wastes. Plants excrete waste through their leaves.
This controls the organism's response to stimuli. It includes the sense organs, brain and nerves. In plants there is no equivalent but there are sensitive regions, e.g. tips of shoots are sensitive to light.
It is made up of bones and muscles for support and movement. The bones can also protect the body. In plants the vascular bundles have supporting tissue next to them. Plant cells use water and the cell wall to support them.
Organs associated with production of sex cells and development of the young. Male organs are different from female organs and are usually in different individuals for animals. In plants both sex structures are usually in the flowers.

Breathing system



What is a cell? Each organ is made up of a series of tissues. The tissues are groups of cells which look alike and carry out a single function in the organ. For example muscle tissue of the heart.
Nucleus: It controls the cell´s activity (like a “control center”) and contains all the genetic information in form of large molecules of deoxyribonucleic acid (DNA). Extra*: is a membrane enclosed organelle found in eukaryotic cells. This part of the cell divides into two when mitosis takes place in order that the new cell has 46 chromosomes identical to the parent cell.
Cytoplasm: A jelly-like substance inside the cell where organelles as mitochondria or vacuoles are placed. It is where most of the cell activities take place. Extra*: In prokaryotic cells the genetic information is in the cytoplasm.
Cell membrane: It is the covering of the cell that keeps it together. It acts as a “gatekeeper”, because it controls what goes into and out of the cell (this characteristic is known as selectively-permeability). Although it protects the cell from bursting, if too much water enters the cell it will burst.

The animal cell structure is less complicated that the plant cell structure because there are more organelles adapted to their functions.

Cell Wall: It is made of cellulose and gives support to the cell; it has the same function as the cell membrane. Extra*: it can be found in plant cells, algae, bacteria and fungi, but not in animal cells or protozoa.

Permanent vacuole: A large central storage organelle in the cytoplasm of plant cells where sap is stored. Extra*: it digests waste proteins and organelles.

Chloroplasts: they contain chlorophyll that is used to trap the energy of sun rays to produce food. They look like green discs in the cytoplasm. They are founded usually on palisade cells which are on the surface of the leave to trap sunshine.

Cell membrane
Cell membrane
No cell wall
Cell wall
No chloroplasts
Only temporary vacuoles
Permanent sap vacuole
Usually smaller
Usually larger
Food stored mainly as glycogen
Food stored mainly as starch
Variety of shapes
Regular boxes appearance


Animals and plants are made up of many cells (multicellular organisms), but there are other organisms that are formed only by one cell (unicellular organisms). These single-celled have the DNA in the cytoplasm and not in the nucleus. It is though that this kind of organism was the first type of cells to evolve (e.g. bacteria).


Each organ has a different function that is why, the tissues and cells that make them up must be specialised. All the animal cells have the same structure, but organelles (specialised regions in the cytoplasm) and substances can vary to allow the specialised cell to carry out its work.

Ciliated epithelial cells: these are found in the windpipe, bronchi and oviducts. They move mucus that trappes bacteria. They beat in a rhythm to remove the mucus with bacteria from the lungs. Mucus is produced by goblet cells which are among the ciliated epithelial cells.
Sex cells (gametes): The sperm cell and the ovum, both have half of the normal quantity of chromosomes (23 instead of 46), so that when they join together they form a proper cell with the appropriate number of chromosomes. The sperm cell has a long tail to swim quickly and arriving to the ovum as soon as possible and also contains enzymes to digest the ovum´s cell membrane. The ovum is large to store food pendant its long journey through the fallopian tubes.
Red blood cells: They don't have a nucleus so they have more space for haemoglobin to carry oxygen; they are flexible to go easily through the blood vessels. This haemoglobin gives the blood its red colour and is used to transport oxygen.
White blood: They do have nucleus and can change shape. They engulf bacteria and produce antibodies to fight against the diseases. There are 500 times fewer white blood cells than red blood cells
Nerve cells: They are long and they have kind of "branches"(synapses and nerve endings) to carry electrical messages and impulses along the whole body. There are two types sensory neurone (carrying impulses from a receptor to the CNS) and motor neurone ( Carrying impulses from the CNS to a muscle or a gland).
Muscle cell: It is elastic so that it can contract and expand. In addition to this, the cytoplasm contains proteins that slide over each other to help the contraction take place. There are many organelles to release energy needed for contraction.

Muscle cell
Ciliated epithelial cell
White blood cells

Plants have also specialised cells:
Palisade cells: They are in the surface of the leaf, they have chloroplasts to capture light and make food.
Root hair cells: They have large surface due to their single hair that helps absorbing more water and nutrients from the soil.
Xylem vessels: They are hollow columns made of xylem cell that have no nucleus nor cytoplasm, water is carried along them.