cell biology

• Eukaryotic cells


  Plant and animal cells
• What characterises eukaryotic cells? (3)

  Cell membrane, cytoplasm and genetic material enclosed in a nucleus
• Prokaryotic cells


  Bacterial cells
• What characterises prokaryotic cells? (4)

  1. much smaller in comparison

  2. have a cytoplasm and cell membrane surrounded by cell wall

  3. genetic material is a single DNA loop not enclosed in a nucleus

  4. may be 1 or more small rings of DNA called plasmids
• Millimetre


  mm, thousandth of a metre, 10^-3m
• Micrometre


  μm, millionth of a metre, 10^-6m
• Nanometre


  nm, billionth of a metre, 10^-9m
• Nucleus


  Contains genetic information and controls cell's activities
• Cell membrane


  Controls the passage of substances in and out of the cell e.g. glucose and ions
• Cytoplasm


  Where most chemical reactions take place
• Ribosomes


  Where protein synthesis takes place
• Mitochondria


  Where aerobic respiration takes place
• Chloroplasts


  Where photosynthesis occurs because they contain chlorophyll (in plant cells)
• Plasmids


  Small rings of DNA which code for very specific features such as antibiotic resistance (in bacterial cells)
• Most animal cells have... (5)

  1. Nucleus

  2. Cytoplasm

  3. Cell membrane

  4. Mitochondria

  5. Ribosomes
• In addition to the parts found in animal cells, plant cells often have...

  1. Chloroplasts

  2. Permanent vacuole filled with cell sap
• Plant and algal cells also have...

  ...a cell wall made of cellulose which strengthens the cell
• Equipment for microscopy practical (6)

  1. Microscope

  2. Onion

  3. Scalpel

  4. Forceps

  5. Slide and cover slip

  6. Iodine
• What must you remember when you are drawing cells from a microscope? (2)

  1. Draw in neat pencil lines

  2. Note down what magnification you are using
• Microscopy practical


  1. Cut a thin sample of onion with the scalpel and place it on the slide

  2. Add a few drops of iodine

  3. Carefully place a cover slip on top, avoiding air bubbles

  4. Place the slide onto the stage

  5. Select the lowest-powered objective lens

  6. Use the coarse adjustment (/focus?) and then fine adjustment knob to focus your image

  7. If necessary, select a higher-powered objective lens and refocus
• How are sperm cells adapted for their function? (5)

  1. Function: to swim to and fertilise an egg cell

  2. Lots of mitochondria in middle section provide energy to tail

  3. Tail is long and contains muscle-like proteins for swimming

  4. Acrosome (head) stores digestive enzyme for breaking down outer layers of egg

  5. Large nucleus contains genetic information to be passed on
• How are nerve cells adapted for their function? (4)

  1. Function: to transmit messages from one part of the body to another

  2. Axon is very long so easier to communicate over further distances

  3. Dendrites (branched endings) allow connections with many other neurones

  4. Nerve endings contain lots of mitochondria to provide energy to make transmitter chemicals
• How are muscle cells adapted for their function? (4)

  1. Function: to generate movement

  2. Contain many mitochondria to transfer the energy needed

  3. Can store glycogen which can be used in respiration to transfer the energy needed

  4. Contain special proteins that slide over each other making the fibres contract
• How are root hair cells adapted for their function? (4)

  1. Function: to absorb minerals and nutrients from the soil

  2. Increased surface are for water to move into the cell

  3. Large permanent vacuole speeds up the movement of water by osmosis

  4. Many mitochondria to transfer the energy needed for active transport
• How are xylem cells adapted for their function? (3)

  1. Function: to carry water and mineral ions from the roots to the rest of the plant

  2. Coated in lignin which kills cells, waterproofs them and creates a long hollow tube

  3. Spirals of lignin make them strong to withstand water pressure and support stem
• How are phloem cells adapted for their function? (3)

  1. Function: to transport sugar from the leaves to the rest of the plant (translocation)

  2. Cell walls between cells form sieve plates (tiny holes) which allow dissolved food to move between cells

  3. Supported by companion cells which have mitochondria to transfer energy for translocation
• Why is cell differentiation important?

  So that cells can become specialised for a particular function and carry out this function in the most efficient way
• When do most types of animal cells differentiate?

  At an early stage
• Many types of plant cells...

  ...retain the ability to differentiate throughout life
• How is cell division restricted in mature animals?

  Cell division is mainly restricted to repair and replacement
• What happens as a cell differentiates?

  It acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell
• Light microscopes


  1. Use a beam of light and lens to form an image

  2. Can magnify up to around 2000 times

  3. You can see individual cells and nuclei
• Electron microscopes


  1. Invented in 1930s

  2. Use beams of electrons to form an image

  2. Can magnify up to 2,000,000 times - subcellular structures

  3. Transmission microscopes give 2D images with high magnification and low resolution

  4. Scanning electron microscopes give 3D images but with a lower resolution
• Resolution


  The ability to distinguish between 2 points
• Magnification


  How small you can go
• Why can an electron microscope be used to study cells in much finer detail than with a light microscope?

  It has a much higher magnification and resolving power
• What have electron microscopes enabled biologists to see and understand?

  Many more sub-cellular structures
• Magnification =


  size of image/size of real object
• How do bacteria multiply?

  Simple cell division (binary fission)
• How often do bacteria multiply?

  Up to every 20 minutes, if they have enough nutrients and a suitable temperature