Revision for AS OCR Biology – Topic 1

Does what i says on the tin :P

Cell structure etc


Light Microscope:

· Mag. down to 2000x

· Resolution down to 0.2 micrometers

·Living tissue can be examined

·Natural colours can be seen

· Mobile

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Electron Microscope:

· Mag. down to 500,000 x

· Resolution down to 0.5 nanometers

· Kills living tissue

· Natural colours cannot be seen

· Can't be moved around

· Very expensive

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  • Site where aerobic respiration takes place.
  • Double membrane,
  • - outer membrane is simple and quite permeable.
  • - Inner membrane is highly folded to form cristae which give it a large surface area.
  • The space inside the inner membrane is known as the matrix.
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The solution inside the cell membrane. Contains enzymes from respiration and other metabolic reactions together with salts, sugars, nucleotides and amino acids.

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Largest organelle. Surrounded by a nuclear envelope which is a double membrane with pores in it containing proteins which control the exit of substances such as RNA and ribosomes. The interior is known as the nucleoplasm which has a lot of chromatin (a DNA/Protein complex in 2:1 ratio containing genetic material). The dark region is known as the nucleolus which is involved in making ribosomes.

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Site where photosynthesis happens. Has a triple membrane, third being the thylakoid membrane which folds into thylakoid disks, which is stacked into a pile known as the grana. the space between the thylakoid disks and the inner membrane is known as the stroma. thylakoid membrane contains the pigment chlorophyll, which is where photosynthesis takes place.

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Site where protein synthesis takes place. Composed of RNA and protein and is manufactured in the nucleolus. Ribosomes are either free in the cytoplasm, where they make proteins to be used by the cell, or are attached to ribosomes, where they make protein to be exported out of the cell.

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Series of membrane channels involved in synthesising and transporting substances, like lipids, needed by the cell.


Studded with Ribosomes. The ribosomes synthesis proteins , which are processed by the RER and exported out of the cell via the Golgi Apparatus.

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Golgi Apparatus:

A series of flattened membrane vesicles called the cisternae. The Golgi Apparatus modifies and packages the protein from the RER to the cell surface membrane by secreting a vesicle.

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A small membrane-bound sac formed from the ER. Contains powerful digestive enzymes which break down unwanted toxins and pathogens.

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A pair of short microtubules involved in cell division. Before cell division, the centriole replicates and the two move to opposite ends of the cell and separate the chromosomes.

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A long and flexible tail present in some cells. It is an extension of the cytoplasm surrounded by a cell membrane. Contain lots of microtubules and motor proteins for complex movement.

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Cell Membrane:

A thin and flexible layer around every cell, made up of phospholipid and proteins. Separates the content of the cell from the outside environment and controls what leaves and enters the cell.

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Protein Production

· The instructions to make a protein are in the DNA in the nucleus.

· The specific instruction to make a protein is known as the gene for that protein. A gene is on a chromosome.

· The nucleus copies the instruction into a molecule called mRNA.

· The mRNA molecule then leaves the nucleus through the nucleus pore and attaches to a ribosome.

· The ribosome reads the instructions and uses the code to assemble the protein.

· The assembled protein in the RER is processed and pinched off in a vesicle and transported to the Golgi Apparatus.

· The Golgi Apparatus modifies and packages the protein ready to be released. The packaged protein is then pinched off in a vesicle and transported to the cell membrane to be secreted out.

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Organelles are surrounded by cytoplasm. Cytoplasm contain a network of protein threads called Cytoskeleton. There are two types 1) Microtubules - Tiny Protein Cylinders 2) Microfilaments - Small Solid Strands.

· Strengthen the cell and maintain its shape.

· Microtubules and Microfilaments support the organelles by keeping them in position.

· Responsible for transporting materials around the cell ie. cell division.

· Protein in the cytoskeleton allow movement ie flagella.

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· Small cell (2 micrometer Diameter)

· Few organelles - Mitochondria not present

· Small Ribosome (70S type)

· DNA is circular

· No nucleus - DNA is free in cytoplasm

· Cell wall made of polysaccharide

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· Larger cell (2-200 micrometres Diameter)

· Lots of organelles - Mitochindria present

· Larger Ribosomes (80S type)

· DNA is linear

· Nuclues present - DNA in nuclues

· Animal Cells - No cell wall, Plant cells - Cellulose cell wall, Fungi - Chitin cell wall

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