Biology Paper 1

• Plant Cell - cell wall, vacuole, chloroplasts, nucleus, cytoplasm, cell membrane, mitochondria, ribosomes.
• Animal Cell - nucleus, cytoplasm, cell membrane, mitochondria, ribosomes
• Nucleus - contains genetic material that controls the activities of the cell
• Cytoplasm - gel- like substance where most chemical reactions happen.
• Cell Membrane - holds the cell together and controls what goes in and out
• Mitochondria - these are where most of the reactions of aerobic respiration take place. Respiration transfers energy that the cell needs to work.
• Cell wall - made of cellulose. Supports the cell and strengthens it.
• Vacuole - contains cell sap, a weak solution of sugar and salts.
• Chloroplasts - where photosynthesis occurs,which makes food for the plant. contain a green substance called chlorophyll,which absorbs the light needed for photosynthesis.
• Bacteria Cells - are prokaryotes
• Bacteria Cell - cell wall,cell membrane, cytoplasm, circular strand of DNA that floats in cytoplasm, small rings of DNA called plasmids.
• Eukaryotes are complex and include all animal and plant cells
• Prokaryotes cells are smaller and simpler e.g. bacteria
• Magnification = image size / actual size
• Light microscopes use light and lenses to form an image,you can see individual cells and large subcellular structures
• Electron microscopes use electrons,they have higher magnification and resolution than light microscopes, can see internal structures like chloroplasts and mitochondria
• Cell Differentiation: The process by which a cell changes from one type of cell to become specialised
• Most differentiation occurs as organisms develop
• In most animal cells,the ability to differentiate is lost at an early stage,after they become specialised
• Lots of plant cells dont ever lose the ability to differentiate, so they can keep growing
• The cells that differentiate in mature animals are used for repairing and replacing cells,such as skin and blood cells
• Some cells are undifferentiated cells - they're called stem cells
• SPERM CELLS - long tail and streamlined head to help it swim. Lots of mitochondria to provide the energy needed. Carries enzymes to digest egg cell membrane
• NERVE CELLS - Carry electrical signals from one part of the body to another. Have branched connections at their ends to connect to each other and form a network.
• MUSCLE CELLS - contract quickly,cells are long (space to contract) contain lots of mitochondria to generate energy needed for contraction
• PHLOEM AND XYLEM CELLS - tubes which transport food and water around plants. To form the tubes,the cells are long and joined end to end. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures,so that stuff can flow through them.
• ROOT HAIR CELLS - on the surface of plant roots,grow into long hairs that stick out into the soil. Big surface area for absorbing water and minerals from the soil
• Nucleus contains genetic material in the form of chromosomes
• Chromosomes are coiled up lengths of DNA molecules
• Each chromosome carries a large number of genes,which control the development of different characterisitics
• Body Cells normally have two copies of each chromosome - one from each parent.
• 23 pairs of chromosomes
• CELL CYCLE - body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle.
• Stage of cell cycle when the cell divides is called mitosis
• Multicellular organisms use mitosis to grow or replace cells that have been damaged.
• The end of the cell cycle results in two new cells identical to the original cell,with the same number of chromsomes
• CELL CYCLES - Growth & DNA Replication - in a cell that's not dividing,the DNA is all spread out in long strings.
• CELL CYCLES - Mitosis - once its contents and DNA have been copied,the cell is ready for mitosis
• DIFFUSION - gradual movement of particles from places where there are lots of them to places where there are fewer of them