AS Edexcel Biology Unit 2 Topic 3

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  • Created on: 21-04-13 13:59


Ribosomes: Floats in the cytoplasm or attached to rER, site of protein synthesis.

DNA: Always circular and not in chromosome form.

Plasmid: Small circles of DNA, contains non-essential genes. Can be exchanged between bacterial cells.

Cell Membrane: Made of phospholipids and proteins, controls movement in and out of the cell. Receptor molecules allow response to chemicals.

Mesosome: Tightly folded region of the cell membrane containing proteins required for photosynthesis and respiration.

Cell Wall: Different from a plant cell wall, made of murein.

Slime Capsule: Used for sticking cells together, and as a food reserve.

Flagellum: A rotating tail used for propulsion.


Cell Membrane: Made of phospholipids and proteins, controls the movement of molecules in and out of cells.

Nucleus: Large organelle surrounded by a nuclear envelope containing many pores. Contains chromatin and a structure called a nucleolus. Chromatin is made of proteins and DNA, controlling cells activities. Pores allow for substances to move between the nucleus and the cytoplasm. Nucleolus make ribosomes.

Ribosome: Small organelle floats in the cytoplasm or attached to rER.

Lysosome: A round organelle surrounded by a membrane. Contains digestive enzymes, used to digest invading cells or to break down worn out components of the cell.

Endoplasmic Reticulum: A system of membranes enclosing a fluid filled space. rER is covered in ribosomes, sER synthesises and processes lipids. rER folds and packages proteins made in the ribosomes.

Golgi: Fluid filled flattened sacs, processes and packages new lipids and proteins, makes lysosomes.

Mitochondrion: Oval shaped, double membrane bound organelle. Inner membrane folds to form cristae. Inside is the matrix containing enzymes for respiration. Site of respiration.

Vesicle: Small fluid filled sac in the cytoplasm, transports substances in and out of the cell. Some are formed by the golgi, some formed at the cell surface.

Centriole: Small hollow cylinders containing a ring of microtubules, involved with the separation of chromosomes.

Protein Production:

1. Proteins are made at the ribosomes.

2. Ribosomes on rER make proteins that are excreted or attached to the cell membrane.

Free ribosomes make the proteins that stay in the cytoplasm.

3. New proteins produced at the rER are folded and processed in the rER.

4. Proteins are transported from the ER to the golgi in vesicles.

5. At the golgi, proteins may undergo further processing.

6. Proteins enter vesicles to be transported around the cell.



Small cells

Large cells

Always unicellular

Usually multicellular

No nucleus or membrane bound organelles

Always have nucleus and other membrane bound organelles

DNA is circular without proteins

DNA is linear and associated with proteins to form chromatin

Ribosomes are small

Ribosomes are large

No cytoskeleton

Has a cytoskeleton

Cell division is binary fission

Cell division by meiosis or mitosis

Asexual reproduction

Asexual or sexual reproduction

Tissues and Organs:

Tissue: A group of specialised cells, all carrying out the same function

Organ: A group of different tissues

Mitosis and The Cell Cycle:

G1: Cells grows and new organelles and proteins are made.  

Synthesis: Cell replicates DNA- ready



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