Key concepts in biology

• What is a prokaryotic cell?

  A cell without a nucleus
• What is a eukaryotic cell?

  cell with a nucleus
• What is the function of the nucleus?

  Contains the cell's genetic material.
• What is the function of the mitochondria?

  use aerobic respiration to transfer energy
• What is the function of the cytoplasm?

  Where chemical reactions take place
• What is the function of the ribosomes?

  site of protein synthesis
• What is the function of the cell membrane?

  to control what enters and leaves the cell
• What is the function of the cell wall?

  to protect and support the cell
• What is the function of the chloroplasts?

  Site of photosynthesis (green pigment chlorophyll absorbs necessary sunlight)
• What is the function of the vacuole?

  Contains cell sap, maintains internal pressure to support the cell.
• What is the function of chromosomal DNA?

  It is one long circular chromosome which controls the cells activities and replication. It floats in the cytoplasm.
• What is the function of plasmid DNA?

  Small loops of extra DNA which aren't part of the chromosome; contain genes for things like drug resistance and can be passed between bacteria
• What is the function of the flagella?

  rotates to help the bacterium move
• How are egg cells specialised?

  They have a large store of nutrients in the cytoplasm, a haploid nucleus and changes in the cell membrane after fertilisation to stop any more sperm getting in
• How are sperm cells specialised?

  long tail and streamline head to help it swim to the egg

  lots of mitochondria in the cell to provide the energy needed

  carries enzymes in its head to digest through the egg cell membrane
• How are ciliated epithelial cells specialised?


  Have small hairs (cilia) which can sweep substances along
• What are the advantages of light microscopes?

  ● Inexpensive

  ● Easy to use

  ● Portable

  ● Observe both dead and living specimens

  - can view specimens in colour
• What are the disadvantages of light microscopes?

  limited magnification and limited resolution
• What are the advantages of electron microscopes?

  Higher magnification and higher resolution
• What are the disadvantages of electron microscopes?

  Expensive, can only view dead specimens, no colour
• How can you calculate magnification?

  magnification = image size/actual size
• How do you view a specimen using a light microscope?

  - thin slice to let light through

  - put drop of water (pipette) on a slide to secure specimen in place

  - place specimen on slide, and place cover slip at an agle to prevent air bubbles

  - put the slip on the stage

  -set to lowest-powered objective lens

  - use coarse wheel to move stage up to just below the obejective lens

  - use fine wheel to bring into focus
• What is an enzyme?

  biological catalyst
• How do enzymes work?

  Lower activation energy needed to start a chemical reaction
• Describe the lock and key model

  The enzyme and the substrate have specific complementary geometric shapes that fit exactly into one another - the substrate fits exactly into the active site. The large insoluble molecules are then broken down into small soluble molecules.
• What happens to enzyme activity as temperature increases?

  At first, enzyme activty increases with temperature, until the optimum is reached. The enzymes and substrates gain more kinetic energy, increasing the likelyhood of a successful collision. Past the optimum, the active site denatures and the substrate no longer fits.
• What happens to enzyme activity as pH increases?

  At first, enzyme activty increases with pH, until the optimum is reached. Past the optimum, the active site denatures and the substrate no longer fits.
• What happens to enzyme activity as substrate concentration increases?

  At first, activity increases because there is a higher likelyhood of a successful collision. However once all active sites are full, activty remains the same
• How can you investigate the effect of pH on enzyme activity?

  - drop of iodine into every spot on a tile

  - heat beaker of water to 35 degrees and keep constant

  - add amylase solution and pH 5 buffer to boiling tube, heat in beaker for 5 minutes

  - add starch solution , mix and start stop clock.

  - everu tne seconds, take a sample and add to a drop, when iodine remains browny yellow instead of blue-black, all the starch has been broken down.

  - stop the stop clock, record time and calculate rate before repeating with buffer solutions of a different pH
• What enzymes break down proteins?

  proteases
• What enzymes break down carbohydrates?

  Carbohydrases eg amylase
• What enzymes break down lipids?

  lipase
• What is starch broken into?

  simple sugars like glucose
• What are proteins broken into?

  amino acids (polypeptides)
• What are lipids broken into?

  fatty acids and glycerol
• What does glycogen sythase do?

  joins together chains of glucose molecules to make glycogen.
• How can you test for sugars?

  Using Benedict's Reagent (blue - green - yellow - brick red)

  - add the reagent to a sample, and heat in a water bath set to 75 degrees.

  - if positive, a coloured precipitate will form

  - higher concentration, more red
• How can you test for proteins?

  Biuret test: use Biuret reagent. Blue to purple if protein is present

  You first need to add potassium hydroxide to make the solution alkaline
• How can you test for lipids?

  Emulsion test - shake sample with ice-cold ethanol, then pour into water. If a precipitation (a milky emulsion) forms, there will be lipids present
• How can you test for starch?

  Add sample to iodine - blue black = starch present