cell biology

• What does a nucleus do?

  It contains genetic material and controls the activities of the cell
• What does cytoplasm do?

  It's a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions
• What does a cell membrane do?

  It holds the cell together and controls what goes in and out
• What do mitochondria do?

  These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work
• What do ribosomes do?

  This is where protein synthesis takes place - where proteins are made in the cell
• What do cell walls do?

  They are made of cellulose and they support and strengthen the cell
• What does a vacuole do?

  It contains cell sap and helps maintain the shape of the cell
• What do chloroplasts do?

  This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis
• What do bacterial cells contain?

  Cytoplasm, cell membrane, cell wall, flagella, ribosomes, mitochondria, slime capsule, plasmids (small rings of DNA) and a single circular strand of DNA that floats freely in the cytoplasm
• What do bacterial cells NOT contain?

  A nucleus
• What is the equation for magnification?

  Image size divided by actual size
• What is differentiation?

  The process by which a cell changes to become specialised for its job
• What are undifferentiated cells called?

  Stem cells
• What are sperm cells specialised for and how are they specialised?

  Reproduction - they transport the male DNA to the female DNA

  -It has a flagella and a streamlined head to help it swim towards the egg

  -There are lots of mitochondria in the cell to provide the energy needed

  -It carries enzymes in its head to help digest through the egg cell membranes
• What are nerve cells specialised for and how are they specialised?

  Rapid signalling - they carry electrical signals from one part of the body to another

  -They are long to cover more distance

  -They have branched connections at their ends to connect to other nerve cells and form a network throughout the body
• What are muscle cells specialised for and how are they specialised?

  Contraction - they need to contract quickly

  -They are long so they have space to contract

  -They contain lots of mitochondria to generate the energy needed for contraction
• What are root hair cells specialised for and how are they specialised?

  Absorbing water and minerals

  -They are cells on the surface of plant roots which grow into long hairs that stick out into the soil

  -They have a large surface area for absorbing water and mineral ions from the soil
• What are chromosomes?

  Coiled up lengths of DNA molecules that are found in the nuclei
• What do multicellular organisms use mitosis for?

  To grow or replace cells that have been damaged
• What are stem cells?

  They are undifferentiated cells that divide to produce lots more undifferentiated cells. They then differentiate into different types of cell
• Where are stem cells found?

  In early human embryos or the bone marrow of adults
• What do embryonic stem cells do?

  1) Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries

  2) Used to replace faulty blood cells
• What is diffusion?

  Diffusion is the movement of particles from an area of high concentration to an area of low concentration
• Name the substances that can diffuse through cell membranes

  Glucose, water, oxygen and amino acids
• Name two substances that can't diffuse through cell membranes

  Protein and starch
• What is osmosis?


  Osmosis is the net movement of water molecules through a partially permeable cell membrane from an area of high water concentration to an area of low water concentration
• What are the two main differences between active transport and diffusion?

  Active transport uses energy whereas diffusion doesn't. Active transport goes against the concentration gradient whereas diffusion goes along it
• Adaptations of Exchange Surfaces

  1) Large surface area - lots of substances can diffuse at once

  2) Lots of blood vessels - to get stuff into and out of the blood quickly

  3) Thin membrane - short distance for substances to diffuse

  4) Often ventilated - air moves in & out
• Give two ways that the villi in the small intestine are adapted for absorbing digested food

  1) A single layer of surface cells

  2) A very good blood supply to assist quick absorption
• Explain how the leaves are adapted to maximise the amount of carbon dioxide that gets into their cells

  1) The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through

  2) The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective

  3) The walls of the cells inside the leaf act as another exchange surface

  4) The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells
• What affects the rate of diffusion?

  Concentration gradient - the steeper the gradient, the faster the rate

  Temperature - the higher the temperature, the faster the rate (the particles have more energy thus move around faster)

  Surface area - the larger it is, the faster the rate

  Diffusion distance - the shorter the distance, the faster the rate
• Examples of active transport

  Plants = Root hairs absorb minerals and water. Each branch of a root will be covered in tiny hairs, therefore increasing the surface area for the absorption of minerals and water. The concentration of minerals is usually higher in the root hair cells than in the soil around them, therefore they can't use diffusion for this process.

  Animals = Glucose is taken in from the gut and from kidney tubules.
• Microscopy Practical - Preparing the Slide


  1) Add a drop of water to the middle of a clean slide

  2) Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers

  3) Using the tweezers, place the epidermal tissue into the water on the slide

  4) Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them

  5) Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view
• Microscopy Practical - Using a Light Microscope

  1) Clip the slide you've prepared onto the stage

  2) Select the lowest-powered objective lens

  3) Use the coarse adjustment knob to move the stage up to just below the objective lens

  4) Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

  5) Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
• Microscopy Practical - Drawing Observations

  1) Draw what you see under the microscope using a pencil with a sharp point

  2) Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines

  3) Your drawing should not include any colouring or shading

  4) If you are drawing cells, the subcellular structures should be drawn in proportion

  5) Include a title & write down the magnification that it was observed under

  6) Label the important features of your drawing using straight, uncrossed lines
• Investigating the Effect of Sugar Solutions on Plant Tissue - Method

  1) Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution

  2) Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours

  3) Take them out, dry them with a paper towel & measure their masses again

  4) If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out, they'll have decreased in mass

  5) The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same
• Possible Errors of the Potato Chip Experiment


  1) Some potato cylinders were not fully dried

  2) Water evaporated from the beakers

  3) The potato chips weren't identical sizes

  4) The volumes of water weren't identical
• Types of eukaryotic cells

  Animal cells

  Plant cells
• What are light microscopes?

  They use light & lenses to form an image of a specimen & magnify it

  Allow us to see individual cells & large subcellular structures e.g. nuclei
• What are electron microscopes?

  They use electrons to form an image

  They have a higher magnification & a higher resolution

  Allow us to see smaller things in more detail e.g. internal structure of mitochondria & chloroplasts & ribosomes & plasmids