Key Concepts

• All living things are made of cells
• Cells can be eukaryotic (nucleus) or prokaryotic (no nucleus)
• Nucleus


  Contains genetic material that controls the activities of the cell. Genetic material is arranged into chromosomes
• Cytoplasm

  Gel-like substance where chemical reactions take place. It contains enzymes that control these reactions.
• Cell membrane

  Holds the cell together and controls what goes in and out
• Mitochondria

  Where most of the reactions for respiration take place. Transfers energy that the cell needs to work.!
• Ribosomes


  There are involved in translation of genetic material in the synthesis of proteins.
• Rigid cell wall

  Made of cellulose. Supports the cell and strengthens it
• Large vacuole

  Contains cell sap, weak solution of sugar and salts. Maintains the internal pressure to support cell.
• Chloroplasts

  Where photosynthesis occurs, makes food for the plant
• Chromosomal DNA

  controls the cell's activities and replication. It floats free in the cytoplasm.
• Plasmid DNA

  Small loops of extra DNA that aren't part of the chromosome. Plasmid contains genes for things like drug resistance, and can be passed between bacteria.
• Flagellum

  A long, hair-like structure that rotates to make the bacterium move. It can be used to move the bacteria away from harmful substances like toxins towards beneficial things like nutrients or oxygen.
• Multicellular organisms contains lots of different types of cells
• Cells that have a structure which makes them adapted to their function are called specialised cells.
• In sexual reproduction, the nucleus of an egg cell fuses with the nucleus of a sperm cell to create a fertilised egg which then develops into an embryo.
• The egg cell contains nutrients in the cytoplasm to feed the embryo; has a haploid nucleus; straight after fertilisation, its membrane changes structure to stop any sperm entering. This makes sure offspring end up with right amount of DNA
• A sperm cell has a long tail so it can swim to the egg; lots of mitochondria in middle section to provide energy needed to swim long distances; acrosome on head where it stores enzymes needed to digest way through membrane of egg cell; contains haploid nucleus
• Epithelial cells line the surface of organs. Some of them have cilia on the surface. Function of ciliated epithelial cell is to move substances in one direction.
• Equation for magnification

  
• Enzymes are biological catalysts. Reduce the need for high temperatures and high pressures.
• Chemical reactions usually involve things either being split apart or joined together.
• The substrate is the molecule changed in the reaction.
• Every enzyme has an active site - the part where it joins on to its substrate to catalyse the reaction.
• Enzymes usually only work with one specific substrate.
• For enzymes to work the substrate has to fit into the active site.
• The enzyme amylase catalyses the breakdown of starch to maltose.
• If starch is present in iodine solution the solution will change to blue-black.
• Digestive enzymes break down food into smaller molecules so that they can be absorbed into the bloodstream
• Enzymes called carbohydrases convert carbohydrates into simple sugars. E.g amylase
• Proteases convert proteins into amino acids
• Lipases convert lipids into glycerol and fatty acids
• Glycogen synthase in an enzyme that joins together lots of chains of glucose molecules to make glycogen.
• Diffusion is the movement of particles from an area of high concentration to an area of low concentration.
• Diffusion happens in both liquids and gases.
• Osmosis is the net movement of water molecules across a partially permeable membrane from high to low concentratio.
• A partially permeable membrane is a membrane with small holes in it.
• Active transport is the movement of particles across a membrane against a concentration gradient from low to high concentration using energy transferred during respiration.
• Active transport allows nutrients to be taken into the blood despite the fact that the concentration gradient is the wrong way. This is essential to stop us starving.