B2 - Scaling Up

• Diffusion


  net movement of particles from an area of high concentration to an area of lower concentration.
• Why is energy not transferred during diffusion?

  During diffusion, particles do not move against the concentration gradient, therefore energy is not needed. Instead, particles move DOWN the concentration gradient making diffusion a PASSIVE process.
• Why does diffusion happen?

  Because molecules are in constant motion
• What do we call materials that only certain molecules can pass through?

  Semi/selectively permeable (partially permeable)
• What is an example of a semi permeable material, and the particles which can pass through it?

  Cell membrane

  Water, Glucose, Amino Acids
• Which particles will not be able to pass through the cell membrane?

  Starch, Proteins
• What are the 4 factors which affect the rate of diffusion?

  1. Concentration Gradient

  2. Distance

  3. Surface Area

  4. Temperature
• How does the concentration gradient affect the rate of diffusion?

  Example?

  A steeper concentration gradient = Faster diffusion

  
  

  Eg: The concentration of CO2 in plant cells will drop, in order to increase the rate of diffusion of CO2 into the cell during photosynthesis (remember, high to low)
• How does distance affect the rate of diffusion?

  Example?

  A shorter distance = Faster diffusion

  - Because particles do not have to travel far.

  
  

  Eg: Blood cappilaries are only 1 cell thick in order to increase the rate of diffusion of gases in and out of the blood.
• How does the surface area affect the rate of diffusion?

  Example?

  Large surface area= Faster diffusion

  - As there is more space for diffusion to take place (more particles can diffuse at one time)

  
  

  Eg: The large intestine is highly folded, increasing the SA in contact with the blood stream. This increases the rate of diffusion of molecules produced during digestion (eg amino acid and glucose)
• How does temperature affect the rate of diffusion?

  The higher the temperature, the faster the rate of diffusion. This is because the particles have more energy so they move around faster.
• Osmosis


  The net movement/ diffusion of water molecules through a selectively permeable membrane, from an area of high water potential to low water potential.
• Water potential


  The concentration of free water molecules as compared to other solute.
• What happens when you place a plant cell in a hypotonic solution?

  hypotonic = low concentration, high water potential.

  
  

  - Water is taken up by the cell by osmosis

  - Pressure of the cell increases (turgor pressure)

  - The cell becomes turgid.
• What happens when you place a plant cell in a hypertonic solution?

  hypertonic = high concentration, low water potential.

  
  

  - Cell loses water by osmosis

  - Turgor pressure falls

  - Cell becomes flaccid (soft)

  - Cell contents eventually collapse away from cell wall

  - The cell is plasmolysed.
• What happens when you place an animal cell in a hypotonic solution?

  - Cell takes up water by osmosis

  - The cell swell up and may burst

  - This is called lysis
• What happens when you place an animal cell in a hypertonic solution?

  - Cell loses water by osmosis

  - The cell crinkles and becomes crenated.
• When may a plant cell be exposed to a hypertonic environment?

  When the soil has not been watered or there is drought.
• What happens when an animal cells gains too much water?

  It will not function efficiently.
• What is a practical for osmosis?

  What is its objective?

  Potato cylinders.

  Show the effect of osmosis on plant tissues
• How do you do this experiment?

  - Prepare a range of sucrose/salt solutions (and 1 with distilled water) with varying concentrations, and place them in boiling tubes.

  - Using a cork borer, create potato cylinders of equal length.

  - Weigh the potato cylinders

  - Way the potato cylinders after being in the boiling tubes

  - Present your results in a table.
• Active Transport


  The movement of molecules across a membrane against the concentration gradient (low to high) (requires energy)
• Where does the energy needed in active transport come from?

  Respiration (in the mitochondria) (ATP)
• What are carrier proteins?

  Special proteins that span across the width of the cell membrane.
• How do carrier proteins work?

  - A large molecule attaches to a carrier protein in the membrane.

  - The protein changes shape/rotates.

  - This releases the molecule on the opposite side of the membrane (into or out of the cell)
• How is active transport used in root hair cells?

  - Plants need water and minerals from the soil in order to survive.

  - These minerals include magnesium ions and nitrate ions.

  - The concentration of these ions are higher in the root hair cell than in the soil

  - The ions are actively transported from the soil into the cell as they cannot be absorbed by diffusion.
• How are root hair cells adapted for active transport?

  - They have a large SA

  - They have lots of mitochondria (to provide energy for active transport from respiration)
• Give 2 other examples of active transport.

  Carbohydrates and broken down into glucose during digestion, the glucose goes from the small intestine to the bloodstream (high to low)

  
  

  In nerve cells, potassium ions are actively transported into the cells, and sodium ions are actively transported in using carrier proteins. This process is crucial for nerve impulses.
• Mitosis


  The process by which body cells divide
• What are 3 reasons for mitosis?

  - To repair damaged cells (Repair)

  - To replace worn out cells (Development)

  - To enable an organism to increase in size (Growth)
• Give 3 features of daughter cells?

  - Produced when a parent cell undergoes mitosis

  - Genetically identical to parent cell

  - Clones
• What is the cell cycle?

  The process of cell growth and division.
• What are the 4 stages of the cell cycle?

  1. DNA replication

  2. Movement of chromosomes

  3. Cytokinesis

  4. The growth of the daughter cell
• What happens during DNA replication?

  - The cell grows in size

  - Double helix unzips forming 2 strands with bases exposed

  - Free nucleotides from the nucleas will pair up with the bases according to complimentary base pairing.

  - This forms DNA base pairs

  - There are now 2 identical molecules of DNA.
• What happens during movement of chromosomes?

  (In preparation for cell division, DNA CONDENSES INTO CHROMOSOMES)

  - Chromosomes line up in the centre of the cell.

  - Identical chromosomes (created during DNA replication) are pulled to opposite ends of the cell (poles) by spindle fibres.

  - 2 new nuclei form

  - cytokinesis occurs.
• What is cytokine


  Separation of the parent cell into 2 identical daughter cells:

  The cell membrane 'pinches' between the 2 new nuclei and separates the cell to form genetically identical daughter cells.
• Give an example as to why mitosis needs to occur rapidly all the time.


  You are constantly losing skin cells, mitosis replaces them.
• During the development of an organism, cells differentiate. What does this mean?


  They become specialised. Which means they change shape so they are better adapted to perform a particular function.
• Some cells are so specialised that they only perform one function. What are some examples?

  - Red blood cells

  - Nerve cells

  - Fat cells

  - Leaf palisade cells

  - Root hair cells
• Sperm cells have particular adaptations so that they can perform their function. What is their function, and their adaptation(s)?


  Function: To transfer genetic material from the male to the ovum (egg)

  
  

  Adaptations:

  Flagellum - to propel into ovum

  Lots of mitochondria - In order to respire and transfer energy from the chemical energy store so flagellum can move.

  Acrosome - Stores digestive enzymes in order to break down outer layer of ovum.