* Key Concepts

• All living things are made of cells. Cells can be either eukaryotic or prokaryotic.
• Eukaryotic cells are complex and include all animal and plant cells.
• Prokaryotic cells are smaller and simpler.
• Animal cells contain nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.

  
• Plant cells contain a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, cell wall, large vacuole and chloroplasts.

  
• A Nucleus contains genetic material that controls the activities of the cell.
• Cytoplasm is a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions.
• A Cell Membrane holds the cell together and controls what goes in and out.
• Mitochondria is where most of the reactions for respiration take place.
• Ribosomes are involved in the translation of genetic material in the synthesis of proteins.
• A Cell Wall is made of cellulose. It supports the cell and strengthens it.
• A Large Vacuole contains cell sap - a weak solution made of sugar and salts. It maintains the internal pressure to support the cell.
• Chloroplasts are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll.
• Bacterial cells contain Chromosomal DNA, Ribosomes, Cell Membrane, Plasmid DNA and Flagellum.
• Bacterial cells contain Chromosomal DNA, Ribosomes, Cell Membrane, Plasmid DNA and Flagellum.

  
• Chromosomal DNA controls the cells activities and replication. It floats free in the cytoplasm.
• Plasmid DNA is small loops of extra DNA that aren’t part of the chromosome.
• Flagellum is 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 and towards beneficial things like nutrients or oxygen.
• 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.
• Both the nucleus of an egg cell and of a sperm cell contain half the number of chromosomes that is in a normal body cell - so they are called haploid.
• Epithelial Cells line the surface of organs. Some of them have cilia (hair-like structures) on the top surface of the cell, they move substances along the surface of the cell.
• Microscopes use lenses to magnify images. They also increase the resolution of an image.
• Resolution means how well a microscope distinguishes between two points that are close together.

  A higher resolution means that the image can be seen more clearly and in more detail.
• Light microscopes were invented in the 1950’s. They work by passing light through the specimen. They let us see things like nuclei and chloroplasts and we can also use them to study living cells.
• Electron Microscopes were invented in the 1930’s.

  They use electrons rather than light. They have a higher magnification and resolution than light microscopes, so they let us see much smaller things in more detail like internal structure of mitochondria and chloroplasts.
• How to prepare the Light Microscope to view a Specimen.

  1. Get a clean slide and use a pipette to put one drop of water in the middle, use tweezers to place the specimen on the slide.
  2. Add a drop of stain if the specimen is transparent or colourless - to make it easier to see.
  3. Place a cover slip at one end of the specimen. Press it down gently so that no air bubbles are trapped under it.

  
• How to view a Specimen using a Light Microscope:

  1. Select the lowest-powered objective lens.
  2. Use the coarse adjustment knob to move the stage up so that the slide is underneath the objective lens.
  3. Then, looking down the eyepiece, move the stage downwards until the specimen is nearly in focus.
  4. Adjust the focus with the fine adjustment knob, until you get a clear image, then measure its size.
  5. If you need a greater magnification to see the specimen, swap to a higher-powered objective lens, refocus and calculate the size.
• Total magnification = eyepiece lens magnification x objective lens magnification
• magnification = image size / real size
• Enzymes are catalysts produced by living things.
• 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.

  
• Changing the temperature changes the rate of an enzyme-catalysed reaction. Like with any reaction, a higher temperature increases the rate at first. But if it gets too hot, some of the bonds holding the enzyme together won’t fit anymore. This changes the shape of the active site, so the substrate won’t fit anymore.

  The enzyme is said to be denatured.

  All enzymes have an optimum temperature that they work best at.

  
• The pH also affects enzymes. If it’s too high or too low the pH interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme.

  All enzymes have an optimum pH that they work best at. It is often neutral ph 7 but not always.

  
• Substrate Concentration also affects the rate of reaction - the higher the substrate concentration, the faster the reaction. This is because it‘s more likely that the enzyme will meet up and react with a substrate molecule.

  
• rate of reaction = 1000 / time
• Enzymes break down big molecules like: Proteins, Lipids and some Carbohydrates.
• Enzymes called carbohydrates convert carbohydrates into simple sugars.

  e.g. amylase is an example of a carbohydrase - it breaks down starch.

  
• Proteases convert proteins into amino acids.

  
• Lipases convert lipids into glycerol and fatty acids.