Cell biology

• Active transport


  The movement of substances from a more dilute solution to a more concentrated solution (against a concentration gradient) with the use of energy from respiration.

  Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.
• how are substances transported into and out of cells by diffusion

  The substances more into the cell from an area of higher concentration to an area of lower concentration
• how are substances transported into and out of cells by active transport

  Substances move from a more dilute solution to a more concentrated solution across a concentration gradient. It requires energy from respiration
• how are substances transported into and out of cells by osmosis


  Water moves from a dilute solution to a concentrated solution
• Difference between diffusion, osmosis and active transport

  Diffusion and active transport involve the movement of dissolved solutes, such as sugars or mineral ions, whereas osmosis involves the transport of water only. In diffusion and osmosis, substances move down a concentration gradient. However, active transport moves substances against a concentration gradient.
• Adult stem cell


  A type of stem cell that can form many types of cells.
• Agar jelly


  A substance placed in petri dishes which is used to culture microorganisms on.
• Cell differentiation


  The process where a cell becomes specialised to its function.
• Cell membrane


  A partially permeable barrier that surrounds the cell which controls what enters and leaves the cell
• Cytoplasm


  A gel-like substance in a cell where most chemical reactions take place. Contains enzymes (biological catalysts) and organelles are found in it
• Cell wall


  An outer layer made of cellulose that strengthens plant cells.
• Chloroplast


  Where photosynthesis takes place, providing food for the plant. Contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis.
• Chromosomes


  DNA structures that are found in the nucleus which are made up of genes.
• Concentration gradient


  The difference in concentration between two areas.
• Diffusion


  The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
• Example of diffusion

  oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.
• Factors that affect the rate of diffusion

  concentration gradient

  the temperature

  the surface area of the membrane.
• Surface area : Volume ratio

  A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.
• Explain the need for exchange surfaces and a transport system in multicellular organisms in terms of surface area to volume ratio.

  In multi-cellular organisms the surface area to volume ration is small so they cannot rely on diffusion alone. Instead surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells.
• How the small intestine and lungs in mammals are adapted for exchanging materials

  -In the lungs, oxygen is transferred to the blood and carbon dioxide is transferred to the lungs to be removed.

  -This takes place across the surface of millions of air sacs called alveoli, which are covered in tiny capillaries, which supply the blood

  -Alveoli in the lungs create a very large surface area and the greater the surface area the more particles can move through, resulting in a faster rate of diffusion

  -The alveoli and capillary walls are extremely thin, this provides a short diffusion pathway allowing the process to occur faster

  -The lungs constantly supply oxygen to make blood from the alveoli oxygenated, by exchanging it for carbon dioxide that can be breathed out. This is a constant process meaning the concentration gradient is always steep
• Explain how the small intestines in mammals are adapted for exchanging materials

  -the cells of the small intestine have millions of villi, which are projections which increase the surface area. This means digested food can be absorbed into the blood faster

  -Villi have a single layer of surface cell they also have a good blood supply
• Explain how gills are adapted for exchanging materials


  The gills are where gas exchange takes place in a fish1)Water(containing oxygen) enters the fish through its mouth and passes out through the gills. As this happens oxygen diffuses from the water into the blood ( which is in the gills) and carbon dioxide diffuses from the blood into the water2) Each gill is made of lots of thin plates called gill filaments which give a big surface area for exchange of gases3)These gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more4)The lamellae has lots of blood caplilaries to speed up diffusion5) They also have a thin surface layer of cells to form a short diffusion pathway6)The concentration of oxygen in the water is always higher than that in the blood , so as much oxygen as possible diffuses from the water into the blood (water flows in one direction and blood flows in the other - this means that a steep concentration gradient is maintained as the concentration of oxygen is always much higher in the water - so it will diffuse across.)
• Explain how the roots and leaves in plants are adapted for exchanging materials

  -Different tissues to aid with gas exchange in leaves

  -Carbon dioxide diffuses through stomata for photosynthesis, whilst oxygen and water vapour move out of them

  -The stomata are controlled by guard cells, which change the size of the stomata based on how much water the plant has received

  -the flattened shape of leaves increases the surface area.

  -The air spaces inside the leaf increase the surface area, so more carbon dioxide can enter cells = faster diffusion
• Exchanging materials in multicellular organisms

  In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism's needs. T
• How is the effectiveness of an exchange surface increased

  having a large surface area

  a membrane that is thin, to provide a short diffusion path

  (in animals) having an efficient blood supply (in animals, for gaseous exchange) being ventilated.
• Embryonic stem cell


  A type of stem cell that can differentiate into most types of human cells.
• Eukaryotic cell


  A type of cell found in plants and animals that contains a nucleus.
• Magnification


  How much bigger an image appears compared to the original object.
• Meristematic cells


  A type of stem cell that can differentiate into any type of plant cell quickly and economically
• Benefits of meristems


  Rare species can be cloned to protect from extinction.

  Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
• Mitochondria


  An organelle which is the site of aerobic respiration, providing energy for the cell
• Mitosis


  A type of cell division which produces two genetically identical daughter cells from one parent cell.
• Nucleus


  An organelle found in most eukaryotic cells that contains the genetic material (DNA) of the cell and controls the activities of the cell.
• Organelle


  A specialised structure found inside a cell.
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• Plasmid


  Loops of DNA found in the cytoplasm of prokaryotic cells.
• Prokaryotic cell


  A type of cell found in bacteria that does not contain a nucleus.
• Resolution


  The ability to distinguish two different points in a specimen.
• Specialised cells


  Cells that are adapted to perform a specific function.
• Stem cell


  An undifferentiated cell that can divide to produce many specialised cells of the same type. Treatment with stem cells can help conditions such as diabetes and paralysis