B2

• What is differentiation?


  Differentiation is the process by which a cell changes to become specialised for its job.
• What is an example of differentiation in plants?


  Palisade leaf cells carry out photosynthesis as they contain chloroplasts. Their tall shape means that they have a lot of surface area exposed down the side for absorbing carbon dioxide from the air in the leaf, and their thin shape means that you can fit loads of them in at the top of a leaf, so they're nearer the light.
• What is an example of differentiation in animals and humans?


  A sperm's function is to get the male DNA to the female DNA during reproduction. Sperm have long tails and streamlined heads to help them swim, they contain lots of mitochondria to provide them with energy and they have enzymes in their heads to digest through the egg's cell membrane.
• Mitosis


  The reproduction of cells by splitting to form 2 identical offspring. It is done so our body can grow and replace damaged cells.
• The Period of Cell Growth and Replication:


  Mitosis (M) - The cycle starts and begins here.

  Gap Phase 1 (G₁) - Cell grows and new cell structures and proteins are made

  Synthesis (S) - Cell replicates its DNA so that when it splits during mitosis the 2 new cells will contain identical DNA

  Gap Phase 2 (G₂) - Cells keep growing and proteins needed for cell division are made

  
• Stages of Mitosis:

  
• Differentiation


  Process in which cells become specialized in structure and function.
• Examples of Specialised Cells: Sperm Cell


  Function: To pass on the necessary biological information required to produce a new organism.

  Structures within a Sperm Cell:

  • Flagellum - Makes the sperm cell move (tail-like)

  • Lots of Mitochondria - Provides energy (ATP) through respiration, needed to sustain sperm motility

  • Acrosome - Contains digestive enzymes to break down the egg's membrane to allow the sperm's entry

  
• Examples of Specialised Cells: Red Blood Cells


  Function: To transport oxygen around the body.

  Structures within a Red Blood Cell:

  • Haemoglobin - Protein that binds to oxygen

  • No Nucleus - More room to store haemoglobin

  • Biconcave Disc Shape - Increases surface area to volume ratio to increase the rate of diffusion

  
• Examples of Specialised Cells: Ciliated Cells


  Function: To move mucus that contains bacteria and dirt.

  Structures within a Ciliated Cell:

  • Goblet Cells - Make mucus to trap dirt and bacteria. It is then swept away to the back of the throat by the cilia.

  
• Examples of Specialised Cells: Palisade Cells


  Function: Site of photosynthesis.

  Structures within a Palisade Cell:

  • Lots of Chloroplasts - To perform its function of photosynthesis

  • Regular Shape - To allow it to be packed into the leaf of the cell

  • Found Near the Surface of a Leaf
• Stem Cells

  Unspecialized cells that retain the ability to become a wide variety of specialized cells.
• The 2 Types of Stem Cells:

  Embryonic Stem Cells

  Adult Stem Cells
• Embryonic Stem Cells


  - Found in early human embryos

  - Divide by mitosis

  - Can differentiate into any specialised cells
• Adult Stem Cells


  - Found in tissues: Brain, Bone Marrow, Skin and Liver

  - Can only differentiate into some cell types

  - Used to repair damage
• Meristems


  - Meristems produce unspecialised cells

  - Found in shoot tips, root tips, and buds

  - The only plant cells that divide by mitosis are found here
• Diffusion


  The passive, net movement of particles from an area of higher concentration to an area of lower concentration. Moving DOWN a concentration gradient.

  
• Active Transport


  The movement of particles across a membrane AGAINST a concentration gradient, from an area of lower concentration to an area of higher concentration, using ATP released during respiration.

  
• Osmosis


  The net movement of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential. Moving DOWN a concentration gradient.

  
• Water Potential


  The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.
• Turgid vs. Flaccid Cell

  
• Effects of too Much or too Little Water on a Cell:

  
• Investigating Osmosis:


  1. Cut equal-sized pieces of potato

  2. Blot with tissue paper and weigh

  3. Put pieces into different concentrations of sucrose solution for a few hours

  4. Remove, blot with tissue paper, and reweigh

  5. Calculate % Change in mass and then plot a graph with your results
• 3 Factors that Affect the Movement of Substances


  - Surface Area to Volume Ratio

  - Temperature

  - Concentration Gradient
• Factors that Affect the Movement of Substances: Surface Area to Volume Ratio

  The rate of diffusion, osmosis and active transport is higher in cells with a larger surface area to volume ratio.
• Factors that Affect the Movement of Substances: Temperature


  As the particles in a substance get warmer they have more energy - so they move faster. This means as temperature increases, substances move in and out of cells faster.
• Factors that Affect the Movement of Substances: Concentration Gradient


  Substances move in and out of a cell faster if there's a big difference in concentration between the inside and outside of the cell. If there are lots more particles on one side, there are more there to move across.
• Transport in Multicellular Organisms

  They have a small surface area to volume ratio so the rate of diffusion would be slow and therefore not fast enough to transport substances around, hence why they have specialised exchange organs.
• Exchange Organs


  An organ (e.g. the lungs) specialised to exchange substances. They are usually very thin, have a large surface area and in animals, have lots of blood vessels.

  
• Gas Exchange in the Lungs


  The alveoli are specialised to maximise diffusion of oxygen and carbon dioxide.

  - O₂ concentration is higher in the lungs than in the blood, so O₂ diffuses into blood

  - CO₂ concentration in the blood s higher than in the lungs, so CO₂ diffuses out of blood

  
• Gas Exchange in Leaves


  When plants respire they use up oxygen and produce carbon dioxide. They keep their stomata open just enough to allow photosynthesis to take place, but not to much so they don't lose excessive water
• Active Transport in Root Hair Cells


  The root hair cells have carrier proteins in their cell membranes. These pick up the mineral ions and move them across the membrane into the cell against the concentration gradient. Because active transport moves ions against the concentration gradient into the root hair cells, energy is needed.
• The Double Circulatory System


  1. In the first one, the heart pumps deoxygenated blood to the gas exchange surfaces in the lungs to take in oxygen. The oxygenated blood then returns to the heart.

  2. In the second one, the heart pumps oxygenated blood around all the other organs of the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again.

  
• Blood Flow


  Blood flows in through the veins and out through the arteries.

  1. Blood flows in through the vena cava and the pulmonary vein.

  2. The blood goes into the aorta and the aorta contracts allowing the blood to flow into the ventricles.

  3. The ventricles then contract to push the blood out of the pulmonary artery and the aorta

  
• Arteries


  Carry blood away from the heart.

  - The heart pumps blood out at high pressure so the artery walls are strong and elastic

  - Thick walls

  - Contain thick layers of muscle to make them strong and elastic fibers to allow them to stretch

  - Arteries branch into arterioles
• Capillaries


  A microscopic vessel through which exchanges take place between the blood and cells of the body.

  - Arterioles branch into capillaries

  - Very tiny (only 1 cell thick)

  - They have permeable walls, so substances can diffuse in and out

  - They supply food and oxygen and take away waste like CO₂

  - Capillaries branch into venules
• Veins


  Blood vessels that carry blood back to the heart.

  - Venules join up to form veins

  - The blood is at a lower pressure in the veins so the walls are not s thick as artery walls

  - Large lumen to help blood flow despite low pressure

  - Have valves to help the blood flow in the right direction
• Blood


  A connective tissue with a fluid matrix called plasma in which red blood cells, white blood cells, and cell fragments called platelets are suspended.
• Plasma


  Liquid part of blood, made mostly of water, in which oxygen, nutrients, and minerals are dissolved.
• Platelets


  Platelets are colorless blood cells that help blood clot. Platelets stop bleeding by clumping and forming plugs in blood vessel injuries.