Unit 1 - Cell level systems

• Eukaryotes or Prokaryotes

  • Eukaryotes - all animals and plants are made from complex cells called eukaryotic cells.
  • Prokaryotes - bacteria are smaller and simpler cells called prokaryotic cells.
  • Both type of cells contain sub-cellular structure - parts of a cell that each have a specific function.
• Animal cells

  • Nucleus - contains DNA in the form of chromosomes that controls the cells activities.
  • Cytoplasm - gel-like substance where most of the chemical reactions happen.
  • Mitochondria - these are the sire for cellular respiration and contain the enzymes needed for reactions involved.
  • Ribosomes - these are where proteins are made in the cell.
  • Cell membrane - holds the cell together and controls what goes in and out.
  • They also contain receptor molecules that are used for cell communication.
• Plant Cells

  • Plant cells include everything animal cells have; nucleus, cytoplasm, mitochondria, ribosomes, cell membrane. As well as:
  • A rigid cell wall - made of cellulose, gives support for the cell.
  • Chloroplasts - where photosynthesis occurs. The contain a green substance called chlorophyll.
• A bacteria cell

  • Chromosomal DNA - one long circular chromosome controls the cells activities and replication. It floats free in the cytoplasm.
  • Plasmids - small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance and can be passed between bacteria.
  • Cell membrane - controls what goes in and out. The cell is also supported by a cell wall.
• Parts of a light microscope

  • Eyepiece lens - looked through to see the image.
  • Objective lens - magnifies the image.
  • Stage - supports the slide.
  • Clip - holds the slide in place.
  • Handle - to carry the microscope with.
  • Lamp - shines light through the slide so the image can be seen.
  • Focusing knobs - moves the stage up and down to bring the image into focus.
• Magnification equations

  • Total Magnification = eyepiece lens x objective lens
  • Magnification = image size / real size
• DNA

  • DNA contains all of the organisms genetic material. DNA is arranged into chromosomes.
  • Chromosomes are long molecules of coiled up DNA. The DNA is divided up into short sections called genes.
  • DNA is a double helix. Each of the two DNA strands is made up of nucleotides joined together in a long chain - this makes DNA a polymer.
  • Each nucleotide contains a small molecule called a base. DNA has 4 different bases.
• The Bases

  • The bases are; A(adenine), C(cytosine), G(guanine), T(thymine)
  • Each base forms cross links to a base on the other strand. This keeps the two DNA strands tightly wound together.
  • A always pairs with T
  • C always pairs with G
  • This is called complementary base pairing.
• Nucleotides

  • Contains a sugar, a phosphate group and a base. Each DNA nucleotide has the same sugar and a phosphate group. The base on each nucleotide is the only part of the molecule that varies.
  • The base is attached to the sugar.
• Polymer

  • Polymers are a large, complex molecules composed of long chains of monomers joined together.
  • Monomers are small, basic molecular units.
  • DNA is a polymer made up of nucleotide monomers.
• Catalysts

  • A substance that speeds up a reaction, without being changed or used up in the reaction itself.
• Enzymes control cell reactions

  • Cells have thousands of different chemical reactions going on inside them. They make up the cells metabolism.
  • These need to be carefully controlled, however you can make a reaction quicker by raising the temperature.
  • There's a limit on how high you can raise the temperature before it gets damaged.
  • So living things produce enzymes, which act as biological catalysts.
  • Each enzyme is a protein coded for by a different gene, and has a unique shape.
• Enzymes

  • Chemical reactions usually involve things being split apart or joined together. The substrate is the molecule changed in the reaction.
  • Every enzyme has an active site. However, they usually only work with one substrate.
  • This is because, for the enzyme to work, the substrate has to fit into the active site. If it doesn't the reaction won't be catalysed. This is called the lock and key hypothesis.
• Temperatures affect on enzymes

  • When the temperature increases, so does the rate of reaction, as cells are more likely to meet up.
  • But, if it gets too hot some of the bonds holding the enzyme together break.
  • This makes the enzyme become denatured. The substrate doesn't fit in the active site anymore.
  • This means the enzyme can't catalyse the reaction, so it stops.
  • It is irreversible.
• How the PH affects enzymes

  • If the PH is too high or too low it interferes with the bonds.
  • This changes the shape of the active site and can irreversibly denature.
• How enzyme concentration affects the rate of reaction

  • The more enzyme molecules there are in a solution, the more likely a substrate molecule will meet up with one and join it. So increasing the concentration of the enzyme increases the rate of reaction.
  • But, if the amount of substrate is limited, there comes a point when there's more than enough enzymes to deal with the available substrate, so adding more enzymes has no further effect.
• Respiration

  • Respiration is the process of transferring energy from the breakdown of glucose. It goes on in every cell in all living organisms.
  • The energy transferred by respiration can't be directly used. so it makes a substrate called ATP, which stores energy.
  • Respiration is controlled by enzymes, so the rate of respiration is affected by both temperature and PH. It's an exothermic reaction - it transfers energy to the environment by heat.
• Aerobic respiration

  • Aerobic respiration is what happens when there's plenty of oxygen available.
  • This is the type of respiration you use most of the time.

  glucose + oxygen ---> carbon dioxide + water

  C6H12O6 + 6O2 ---> 6Co2 + 6H2O
• Anaerobic respiration

  • Anaerobic is respiration without oxygen.
  • It is slightly different in different organisms.
• Anaerobic respiration in animals

  • When you're vigorously exercising your body can't supply enough oxygen for aerobic respiration, so you start respiring anaerobically.
  • In anaerobic respiration glucose isn't broken down fully, so lactic acid is produced.
  • glucose ---> lactic acid
  • Lactic acid build up in the muscles, so when you stop exercising you have oxygen debt.
  • this means you need extra oxygen to breakdown the lactic acid that's built up to allow aerobic respiration to begin again.
• Anaerobic respiration in plants and fungi

  • Under certain conditions plants may also resort to anaerobic respiration.
  • E.g. waterlogged soil, where there is little to no oxygen, plant root cells will respire anaerobically.
  • Some fungi, such as yeast, respire anaerobically too.
  • Anaerobic respiration in plants and fungi; produces ethanol and carbon dioxide instead of lactic acid.
  • glucose ---> ethanol + carbon dioxide
• Differences and similarities between aerobic and anaerobic

  Aerobic Anaerobic

  Conditions: Oxygen present Not enough oxygen present

  Substrate: Glucose

  products: Carbon dioxide Plant / fungi - carbon dioxide /ethanol

  and water Animals - lactic acid

  Energy 32 ATP 2 ATP

  transferred:
• Carbohydrates

  • Carbohydrates molecules contain the elements carbon, hydrogen and oxygen.
  • The smallest units, monomers are simple sugars.
  • These can be joined together in long chains, polymers, to make large, complex carbohydrates.
  • The polymer molecules can be broken down back into sugars again when the chemical bonds between the monomers are broken.
  • In the body, carbohydrates are broken down (digested) by enzymes in the mouth and small intestine.
• Proteins

  • Proteins are polymers that are made up of long chains of monomers called amino acids.
  • Amino acids all contain carbon, nitrogen, hydrogen and oxygen atoms.
  • In the body, proteins are broken down by enzymes in the stomach and small intestine.
• Lipids

  • Lipids (fats and oils) are made up of glycerol and three fatty acids.
  • Unlike carbohydrates and proteins they are not polymers because they don't form a long chain of repeating units.
  • Lipids contain carbon, hydrogen and oxygen atoms.
  • In the body, lipids are broken down by enzymes in the small intestine.
• Photosynthesis

  Process that uses energy from the sun to make glucose
• Photosynthesis


  1. Energy from the sun is used to split water into oxygen gas and hydrogen ions

  2. Carbon dioxide combines with the hydrogen ions to make glucose
• Photosynthesis


  • Some of the glucose is used to make larger complex molecules that the plants or algae need to grow
  • This makes up their biomass - the mass of a living organism
  • The energy is stored on the organisms biomass then works it's way through the food chain
• Chloroplast


  Where photosynthesis happens inside the plant or algae
• Chlorophyll


  Absorbs light energy for photosynthesis
• Light energy


  Transferred to the chloroplast from the environment
• Photosynthesis

  An endothermic reaction - energy is transferred from the environment during it
• Photosynthesis equation

  Carbon dioxide + water ----> glucose + oxygen

  light

  6Co2 + 6H2O ----> C6H12O6 + 6O2
• How light affects the rate of photosynthesis

  • Light transfers the energy needed for photosynthesis.
  • As the light level is raised, the rate of photosynthesis increases steadily, but only to a certain point.
  • Beyond that, it won't make a difference.
• How carbon dioxide affects the rate of photosynthesis

  • CO2 is one of the raw materials needed for photosynthesis.
  • As with light intensity the concentration of CO2 will only increase the rate of photosynthesis up to a point.
  • CO2 is no longer a limiting factor.
• How temperature affects the rate of photosynthesis

  • Usually if temperature is the limiting factor it's because it's too low - the enzymes needed for photosynthesis work more slowly at low temperatures.
  • But if the plant gets too hoy, the enzymes it needs for photosynthesis and its other reactions will be denatured - the rate of reaction devreases dramatically.