Cell Structure and Transport

• Advantages of a light microscope (3)


  1) Able to view living organisms

  2) Relatively inexpensive

  3) Can be used almost anywhere
• Disadvantages of light microscope (2)


  1. Low magnification (only x2000 and school microscopes can only magnify up to a couple hundred times)

  2. Low resolution
• Advantages of electron microscope (3)


  1) High resolution

  2) Good magnification (x2 000 000)

  3) Different computer viewing capabilities
• Difference between transmission electron microscopes and scanning electron microscopes


  Transmission electron microscopes give 2D images with high magnification and resolution whereas scanning electron microscopes give dramatic 3D images but with lower magnification and resolution
• How to calculate magnification


  Image size/actual size
• What is resolution?


  The ability to clearly distinguish the individual parts of an object
• What is the resolving power of a light microscope?


  200nm
• What is the resolving power of a (1) scanning electron microscope and a (2) transmission electron microscope?


  1) 10nm

  2) 0.2nm
• What are the sub-cellular structures in an animal cell?

  Nucleus - contains the genes and controls activities of the cell

  Cytoplasm - suspends organelles and site of most chemical reactions

  Cell membrane - controls movement of substances in and out of the cell

  Mitochondria - site of aerobic respiration

  Ribosomes - where protein synthesis takes place
• What additional sub-cellular structures do plants have?


  Cell wall - made of cellulose and strengthens the cell giving it support

  Chloroplasts - contains chlorophyll that absorbs light for photosynthesis

  Permanent vacuole - full of cell sap keeping the plant upright
• What are the sub-cellular structures of prokaryotic cells?


  Cell wall, cell membrane, cytoplasm, genetic material, plasmids, flagella, slime capsule
• What are plasmids?


  Plasmids are small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for things like drug resistance and can be passed between bacteria.
• What is a slime capsule


  It's a protective layer around the cell well
• What does the flagella do?


  They're long protein strands that lash about and they're used to move the bacteria around
• Range of eukaryotic cell size


  10µm - 100µm
• What is the average size of a prokaryotic cell?


  1-10 µm
• How are nerve cells specialised? (3)


  1) Lots of dendrites to make connections to other nerve cells

  2) An axon that carries the nerve impulse from one place to another; they can be very long.

  3) They contain lots of mitochondria to provide the energy needed to make the transmitter chemicals that are needed to pass impulses between nerve cells and a muscle
• How are muscle cells specialised? (3)


  1) They contain special proteins that slide over each other making the fibres contract

  2) They contain many mitochondria to transfer the energy needed for the chemical reactions that take place as the cells contract and relax

  3) They store glycogen (chemical that's broken down and used in cellular respiration to transfer the energy needed for fibres to contract)
• How are sperm cells specialised? (4)


  1) Long tail to help move the sperm through water or the female reproductive system

  2) Middle section full of mitochondria which transfer the energy needed for the tail to work

  3) The acrosome stores digestive enzymes for breaking down the outer layers of the egg

  4) Large nucleus containing the genetic information to be passed down
• How are root hair cells specialised? (3)


  1) Large surface area for water to move into the cell

  2) They have a large permanent vacuole that speeds up osmosis

  3) More mitochondria that transfer the energy needed for the active transport of mineral ions
• How are photosynthetic cells specialised? (3)


  1) Chlorophyll in chloroplasts for photosynthesis

  2) Usually positioned on the outer layer of the stem or on leaves to absorb as much sunlight

  3) Large permanent vacuole that keeps the cell rigid as a result of osmosis. They also keep the leaf spread out to capture as much light as possible
• How are xylem cells specialised? (2)


  1) They are hollow in the centre and have very few sub-cellular structures to allow water and mineral ions flow through them

  2) The spirals and rings of lignin make them strong and withstand the pressure of water moving up the plant
• How are phloem cells specialised? (2)


  1) The cell walls between the cells break down to form sieve plates allowing water carrying dissolved food to move freely up and down the tubes where it is needed

  2) They are supported by companion cells that help to keep them alive. The mitochondria of the companion cells transfer the energy needed to move dissolved food up and down the plant in phloem
• What is net movement?


  The overall movement of particles. (particles moving in - particles moving out). It is from an area of higher concentration to lower concentration
• What is a concentration gradient?


  Difference in concentration between two areas and the bigger the difference the steeper the concentration gradient
• What is osmosis?


  Movement of water across a partially permeable membrane from a dilute solution to a concentrated solution
• What does it mean when a concentration is isotonic to a cell?


  Concentration outside cell = concentration inside cell
• What does it mean when a concentration is hypertonic to a cell?


  Concentration outside cell > concentration inside cell
• What does it mean when a concentration is hypotonic to a cell?


  Concentration outside cell < concentration inside cell
• What is turgor pressure?


  The water pressure inside the vacuole of the plant cell in response to the force of water within the cell when water moves into the plant cell
• Why do plants need the fluid surrounding the cell to always be hypotonic to the cytoplasm?


  It keeps the water moving by osmosis in the right direction and the cells turgid otherwise it it is hypertonic it will become flaccid and there will be no pressure on the cell walls meaning no more support for the plant tissues
• What is plasmolysis?


  Shrinkage of a cell due to water being removed due to a hypertonic solution.
• What is active transport?


  Movement of ions or molecules across a cell membrane from low concentration to high concentration against the concentration gradient.
• Why does active transport require so much energy and how does it work?


  Active transport requires lots of ATP because the molecules move against the concentration gradient and this works by one of the bonds in ATP breaking which releases lots of energy
• How is the energy from respiration used?


  By protein transport molecules embedded in the cell membrane to move substances in and out of the cell
• What is the difference between active transport and diffusion? (2)


  1) Diffusion requires no energy whereas active transport does

  2) Diffusion is moving down the concentration gradient whereas active transport moves against it
• Give 2 reasons as to why active transport is important? (2)


  1) Root hair cells taking in minerals from solutions in the soil that are more dilute than in the cell so active transport allows the cell to take in the minerals even though it's against the concentration gradient

  2) Sugar needs to be absorbed out of the gut and kidney tubules into the blood
• What are the (main) ions used by plants?

  Magnesium ions - make chlorophyll

  Nitrate ions - make amino acids therefore used for protein synthesis and subsequently growth
• How is active transport helpful for crocodiles?


  Crocodiles have salt glands in their tongues. These remove excess salt from the body against the concentration gradient. That's why some crocodiles can live in estuaries and the sea.
• What are some adaptations for exchanging materials? (4)


  1) Large surface area over which exchange can take place

  2) Thin to provide a short diffusion path

  3) Efficient blood supply which moves the diffusing substances away from the exchange surfaces and maintains a steep concentration gradient

  4) Ventilation which makes gas exchange efficient by maintaining a steep concentration gradient