B4

• Respiration

  Respiration is the release of energy from sugar molecules such as glucose.
•  How cells use the energy from respiration


  To combine small molecules to make larger molecules

  To break large molecules into smaller molecules

  For muscle contraction

  To maintain our body temperature

  To move substances around the cell
• Metabolism


  The combination of all chemical reactions in an organism 
• Word equation for anaerobic respiration in plants and fungi:

  Glucose ➔ ethanol + carbon dioxide
• What are the two reasons animals cells prefer aerobic respiration to anaerobic respiration?

  Anaerobic respiration doesn't break down the glucose molecule completely, and so releases less energy than aerobic respiration

  Anaerobic respiration produces lactic acid which can damage cells and leads to an oxygen debt
• Steps of mitosis

  1. DNA condenses to form chromosomes.
  2. Chromosomes line up along the centre of the cells.
  3. Cell fibres pull the two arms of each chromosome to opposite sides (poles) of the cell.
  4. Cytokinesis - the entire cell divides to form two identical daughter cells.
• What are the three reasons why new cells are required?

  Growth (we need more cells as we grow)

  Development (we need new cell types as we develop new tissues)

  Repair (we need to replace the cells that we lose each day)
• Steps of the cell cyle

  1. Cellular growth - the cell gets larger and produces more sub-cellular structures, such as mitochondria and ribosomes. 
  2. DNA replication - chromosomes duplicate, so that each consists of two arms (copies).
  3. More cell growth.
  4. Mitosis - the DNA divides into two.
  5. Cytokinesis - the cell divides into two.
• What part of the microscope is highlighted?

  Base

  
• What part of the microscope is highlighted?

  eyepiece lens

  
• What part of the microscope is highlighted?

  slide

  
• magnification


  How many times larger the image is than the object
• What part of the microscope is highlighted?


  objective lenses

  
• pathway of light through a microscope

  Light source ➔ stage ➔ microscope slide ➔ object ➔ objective lens ➔ body tube ➔ eyepiece lens ➔ eye
• What part of the microscope is highlighted?

  stage

  
• magnification = image size / object size
• Sperm and egg cells are haploid cells and only have 23 chromosomes. When a sperm fertilises the egg though, they form a diploid cell that has 46 chromosomes.
• What does the term 'haploid' mean?


  A cell that only has half the normal amount of genetic material
• How many cells are produced during meiosis?

  4
• Two key features of stem cells:

  They can divide by mitosis to form more cells

  They can differentiate into specialised cells
• 1. When a sperm cell fertilises an egg cell they form a single cell called a zygote.
  2. This cell then divides by mitosis to form a ball of cells which we call an embryo.
  3. The cells in this embryo are known as embryonic stem cells and can differentiate into any type of cell. 
• Adult stem cells can only differentiate into different types of blood cells, e.g. white blood cells, red blood cells and platelets. 
• Which two parts of the plant contain meristem tissue?


  Tips of the roots

  Tips of the shoots
• What is the problem in type 1 diabetes?

  The pancreas is damaged and no longer produces insulin
• Paralysis

  When nerve cells are damaged, messages can no longer be sent to the muscles properly. This can lead to the loss of the ability to move some or all of your body.
• Stem cell treatment

  Extract embryonic stem cells from early embryos. Grow them in a laboratory. Stimulate them to differentiate into whichever type of specialized cell that we want. Give them to the patient to replace their faulty cells.
• Drawbacks of using embryonic stems cells in stem cell therapy. 


  The embryonic stem cells must come from embryos. These are in limited supply, and some people have ethical objections to it, as they think the embryos could have developed into a person.

  The cells could be rejected by the person's immune system as it would identify them as foreign.
• Which two of the options below are advantages of using adult stem cells rather than embryonic stem cells?


  Adult stem cells are taken from the patient so are not in limited supply

  Adult stem cells won't cause rejection as they're taken from the patient themselves
• Two risks of using stem cells in medicine 

  The stem cells could be infected with a virus whilst in the laboratory, which could then infect the patient. As stem cells divide quickly, there is a chance they could divide uncontrollably once they've been transplanted, and then develop into a tumour. 
• Explain how a sperm cell is adapted for its role.

  Its role is to deliver genetic material to an egg cell to fertilise it

  It has half as much genetic material as a normal cell, so that the sperm and egg together will have the normal amount

  It has lots of mitochondria to provide the energy for movement

  It has a flagellum to allow it to swim to reach the egg

  It is streamlined to make swimming easier 

  It has digestive enzymes in its head to break through the wall of the egg
• Cells that are adapted to perform a particular function are called specialised cells.
• Auxins are a family of plant hormones produced in the tips of shoots and roots. Once produced, they diffuse backwards along the shoot or root.
• Auxins always accumulate on the:

  lower side

  shaded side
• Shoots are considered:


  positively phototropic

  negatively gravitropic
• Plant roots are:


  They are negatively phototropic but positively gravitropic
• In what direction will the plant grow?

  The shoot will grow towards the left. This is because the light is on the left, and so auxins will accumulate on the right side (which will be in the shade). Auxins stimulate growth in shoots, so the right side of the shoot will grow faster, causing the shoot to lean over to the left.

  
• What happens to make a root grow in the direction of the force of gravity?

  The top side grows more than the bottom side
• What effects do auxins have on plants?


  Shoot cell growth and root cell inhibition
• Plant hormones


  ethene

  auxins

  gibberellin
• What are three uses of auxins in agriculture and horticulture?

  In weedkillers, rooting powders and to promote growth in tissue culture