Biology AQA Unit 2 Summary

Cell Structure: 

• Human & Animal Cell: Nucleus, Cytoplasm, Membrane, Mitochondria, Ribosomes. 

• Plant Cells: Chloroplasts, Cell Wall, Permanent Vacuole, Nucleus, Cytoplasm, Membrane, Mitochondria, Ribosomes. 

• Nucleus – Contains genetic material to control activity in the cell. 

• Cytoplasm – Where chemical reactions occur. Contains enzymes.  

• Cell membrane – Controls what gets in and out. 

• Mitochondria – Where respiration takes place.  

• Ribosomes – Where proteins are made.  

• Cell wall – Made of cellulose – strengthens the cell. 

• Vacuole – Contains cell sap (sugar and salts). 

• Chloroplast – Where photosynthesis occurs. Contains chlorophyll.  

Different Cells:  

• Yeast: Single-celled organism. Microorganism with a nucleus, cytoplasm, cell membrane, and cell wall.  

• Bacteria: Single-celled organism. Cytoplasm, cell membrane, and cell wall. Genetic material is in cytoplasm.  

Diffusion: 

• Movement of particles from a high concentration of the particles to a low concentration.  

• Occurs in liquids and gasses. (Particles are free to move). 

• The bigger the concentration difference, the faster the diffusion. 

Cell Membranes: 

• Allows dissolved substances to move in and out of the cell. (Only small molecules such as oxygen, glucose, amino acids, and water). 

Specialised Cells: 

Cells become specialised through differentiation. Occurs during the development of multicellular organism.  

• Palisade Leaf Cells: Contain a lot of chloroplasts for photosynthesis. More at the top so they are exposed to more light. Tall shape and larger surface area to absorb CO2. Usually grouped together at the top of the leaf. 

• Guard Cells: Opens and closes stomata in a leaf. Stomata opens when the plant has lots of water, so gases can be exchanged for photosynthesis. Guard cells close when the plant is short of water to stop water from escaping. They are sensitive to light and close at night. 

• Red Blood Cells: Concave shape and large surface area for absorbing oxygen. Helps to pass smoothly through capillaries. No nucleus to allow for more haemoglobin. 

• Sperm and Egg Cells: Specialised for reproduction. Egg specialised to carry female DNA and nourish developing embryo. Sperm is designed to get male DNA to female DNA with long tai and streamlined head. A lot of mitochondria to provide energy. Sperm carried enzymes to digest through egg cell membrane. Eggs membrane instantly changes its structure one it has met sperm to stop more sperm from getting in.  

Cell Organisation: 

• Similar cells are organised into tissues to carry out a particular function. Muscular tissue contracts to move whatever it's attached to. Glandular tissue makes and secretes chemicals like enzymes and hormones. Epithelial tissue covers some of the body. 

• An organ is a group of different tissues that work together to perform a particular function. I.E- the stomach... Muscular tissue moves the stomach wall to churn food. Glandular tissue makes chemicals to digest food. Epithelial tissue covers the outside and inside of the stomach. 

• An organ…