SB1

• Eukaryotic cells have a nucleus. Prokaryotic cells are simpler and do not have a nucleus.
• Animal and plants cells have:

  • Nucleus - contains genetic material that controls cell activities.
  • Cytoplasm - gel-like substance where most of the checmical reactions happen.
  • Cell membrane - holds the cell together and controls what goes in and out.
  • Mitochondria - where the reaction for respiration takes place.
  • Ribosomes - where protein synthesis takes place.
• Only plant cells have:

  • Rigid cell wall - made of cellulose, it supports the cell and strengthens it.
  • Large vacuole - contains cell sap, a weak solution of sugar and salts. It maintains internal pressure to support the cell.
  • Chloroplasts - where photosynthesis occurs, which makes food the plant.
• Bacterial cells contain the following:

  • Chromosonal DNA - controls cell activities and replication.
  • Ribosomes - where protein synthesis takes place.
  • Cell membrane - hold the cell together and controls what goes in and out.
  • Plasmid DNA - small loops of extra DNA that holds specific genes.
  • Flagellum - long hair like structure that rotates to make the bacterium move.
• A specialised cell is a cell that has a structure adapted to its function.
• An egg cell carries female DNA and feeds a developing embryo. It contains:

  • nutrients in the cytoplasm
  • haploid nucleus
  • cell membrane changes structure after fertilisation.
• Sperm cells transport male DNA to the egg. It contains:

  • Nutrients in cytoplasm
  • Haploid nucleus
  • Lots of mitochondria to provide energy for swimming
• Cilliated epithetal cells move substances along internal surfaces. It contains cillia which 'beat' to move substances.
• Enzymes are biological catalysts that speed up chemical reactions.
• Each enzyme only catalyses one specific reaction because of the unique shape of its active site.
• The enzyme and its specific substrate will fit together like a lock and key. The enzyme then remains unchanged, and its products are let go.
• Factors affecting enzyme activity:

  • High temperature
  • High and low pH
  • Substrate concentration
• Enzymes break down big molecules into smaller ones which are used for life proceses.
• Protease converts proteins into amino acids.
• Lipase converts lipids into fatty acids and glycerol.
• Amalyse converts carbohydrates into glucose.
• Calorimetry is used to find the amount of energy in food.
• Calculation to find energy in food:

  energy in food (J) = mass of water (g) * temperature change of water * 4.2
• How to perform calorimetry:

  • Weight food sample then put it on a mounted needle.
  • Add set volume of water to boiling tube and record its temperature.
  • Set fire to food, hold it under the boiling tube until it goes out. Repeat until the food no longer catches on fire.
  • Record the temperature of the water.
• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
• Only very small molecules can diffuse across cell membranes.
• Active transport is the movememnt of particles against a concentration gradient. It requires energy from respiration.
• Osmosis is the net movement of water molecules across partially permeable membrane from a region of higher water concentration to a region of lower water concentration.