Biology Revision



All living organisms are made up of cells

Light microscope can magnify 100's of times.

Electron microsope can magnify 100000's of times.

Animal cells:

nucleus- controlls cells activities. Contains instructions for making new cells/organisms. (contains DNA and chromosomes).

Cytoplasm- liquid gel, chemical reactions for life take place eg respiration.

Cell membrane- controls passage of substances in and out of cell.

Mitochondria- structures in cytoplasm where most energy released during repiration.

Ribosomes- for protein synthesis.

Plant cells: All features of an animal cell plus:

Cell wall - made of cellulose, strengthens cell and gives support. (algae also made of cells have cell wall made of cellulose)

Chloroplast- found in green parts of plant, contains chlorophyll, absorbs light to make food by photosynthesis.

Permanent vacuole- Keeps cell ridgid to support plant. (filled with cell sap)

Chemical reactions in cells:

Each reaction is controlled by a enzyme. Enzymes are proteins that conrtol the rate of chemical reactions and make sure each reaction happens separately ( catalyst). We find many enzymes in mitochondria.

Enzymes found in different parts of cell:

Respiration- mitochondria

Photosynthesis- chloroplast

Protein synthesis- ribosomes.

Specialised cells

Palisade cells- found in leaves, contain lots of green chlorophyl to absorb light energy from sun and use it in photosynthesis. Shape is long and thin which helps absorb as much light as possible as it passes through leaf. (palisade mesophylll cell)

Red blood cells- Makes up part of the blood. Has no nucleus so it can hold more red pigment called haemoglobin which carries oxygen from the lungs around the body to cells. Shape is concave, giving it a large surface area to absorb lots of oxygen quickly.

Nerve cells(neurones)- Found in brain and nerves of humans. Have short and long fibres which quickly transmit impulses a long distance from on part of the body to another. Have lots of small branches to make fast connections with other nerve cells.

Ovum/egg - Sex cells of a female and are made in ovaries. Large cells containing lots of food (yolk) to feed a developing embryo. Contain genetic information from mother in their nucleus. Hve a jelly membrane on the outside, making sure only one sperm can penetrate/fertilise it.

Sperm cell- These cells are the sex cells of a male and are made in testes. Very small and dont contain yolk like eggs. Have long tails and streamlined shape so they can swim to ovum. When one meets an ovumit penetrates and fertlises it. Contains gentic information from father.

Ciliated epithelial cells- Cover some inner surfaces of body. Cilia are tiny hair like processes, which constantly beat back and fourth, moving substances through tubes eg moving mucas out of the windpipe and away from lungs.

Root hair cell- Found in the roots of plants. Long hair like processes gives large surface area to help plant root absorb water and minerals. Cell walls are thin to make absorbtion faster. Cells in plant roots do not have chloroplasts because they dont have access to light. Long and narrow to fit…


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