Cell structure and transport

• How much can light microscopes magnify up to

  2000x
• How much can electron microscopes magnify up to

  2 000 000x
• Resolving power of electron microscopes

  10nm (scanning electron microscope)

  0.2 nm (transmission electron microscope)
• resolving power of light microscope

  200 nm
• Suggest why nucleus and mitochondria are so important in all cells

  nucleus - controls all cells activities

  contains instructions for making new cells or new organisms

  mitochondria - site of aerobic respiration, releasing energy for the cell
• Suggest two types of plant cells that are unlikely to have chloroplasts and in each case explain why they have none


  root cells - no exposure to light

  cells in centre of tree trunk - no exposure to light

  cells in flowers of plant - function is not to photosynthesise
• Main function of permanent vacuole?

  keeps cells rigid to support plant
• Main function of cell wall


  strengthens cell and provides support
• What is the function of flagellum

  long protein strand that lashes about and bacteria uses this to move themselves around
• What is the difference between genetic material in a prokaryotic cell and the genetic material in a eukaryotic cell

  -genetic material in prokaryotic cell isn't contained in nucleus

  -may include extra rings of DNA separate from main genetic material
• Similarities and differences between the features found in prokaryotic and eukaryotic plant and animal cells

  -all cells have cell membranes + cytoplasm

  -both prokaryotic and eukaryotic can have cell wall

  -prokaryotes have no nucleus + no chloroplasts

  -whilst eukaryotes have no plasmids
• Adaptations of nerve cell


  -lots of dendrites to make connections to other nerve cells

  -long axon that carries nerve impulse from one place to another

  -synapses adapted to pass impulses to another cell or between nerve cell using special transmitter chemicals
• Adaptations of striated muscle cells

  -contain special proteins that slide over each other making the fibres contract

  -lots of mitochondria to transfer energy needed for chemical reaction to take place

  -stores glycogen, broken down and used in cellular respiration by mitochondria to transfer energy needed for fibres to contract
• Adaptations of sperm cell

  -long tail to move sperm through water or female reproductive system

  -lots of mitochondria in middle section transfer energy needed for tail to work

  -acrosome stores digestive enzymes for breaking down outer layers of egg

  -large nucleus contains genetic information to be passed on
• Why do nerve cells have lots of mitochondria

  transmitter chemicals are required to pass impulse from one nerve cell to another

  lots of mitochondria supply energy for cellular respiration needed to make transmitter chemicals
• Describe features you would look for to decide on the function of an unknown specialised animal cell

  number of mitochondria - indicates how much energy cell uses

  flagella or cilia - indicates whether cell moves around or moves substances such as mucus

  nucleus - indicates whether cell is capable of reproduction

  storage materials (fat or starch) - indicates whether cell stores materials it can use for respiration
• Root hair cell adaptation

  increased surface area - water to move into cell

  large permanent vacuole - speeds up movement of water by osmosis from soil across root hair cell

  mitochondria - energy for active transport of mineral ions into root hair cells
• Photosynthetic cells adaptation

  chlorophyll - trap light needed for photosynthesis

  positioned in continuous layers of leaves and outer layers of stem of a plant - absorb as much light as possible

  large permanent vacuole - keep cell rigid as result of osmosis, supports stem
• Adaptation of xylem cells

  lignin causes cells to die - form long hollow tubes that allow water and mineral ions to move easily through them

  spirals + rings of lignin - make xylem cells very strong and withstand pressure of water moving up the plant
• Adaptations of phloem cell

  cells walls between cells break down to form special sieve plates - allow water carrying dissolved food to move freely up and down tubes

  phloem cells lose a lot of internal structure but are supported by companion cells to keep them alive - mitochondria of companion cells transfer energy needed for movement of dissolved food up and down phloem
• Suggest why a cell within the trunk of a tree cannot carry out photosynthesis

  Cell not exposed to sunlight

  Therefore not adapted to carry out photosynthesis
• Describe features you would look for to decide on function of an unknown specialised plant cell

  Chloroplasts - indicates whether cell is photosynthetic

  Large vacuole - indicates role in osmosis/ rigid support

  Lignin spirals - indicates strengthening and transport of water

  Sieve plates/ companion cells - indicates transport of dissolves food

  Mitochondria - indicates active movement of substances
• What is diffusion

  Overall net movements of particles from a high concentration to a low concentration, down a concentration gradient
• Why does diffusion take place faster when there is an increase of temperature?

  Heating makes particles move more quickly

  Speeding up diffusion as particles collide more often and harder and spread out faster
• What is hypertonic

  Concentration of solutes in solution outside cell is higher than internal concentration
• What is hypotonic

  Concentration of solutes outside cell is lower than internal concentration (more dilute outside)
• What is turgor pressure?

  -Water moving into plant cells by osmosis

  -Causes vacuole to swell and press cytoplasm against cell wall

  -Pressure builds up so no more water can physically enter the cell
• What is plasmolysis?

  -Water is continually lost by osmosis, vacuole and cytoplasm shrinks and eventually cell membrane pulls away from cell wall
• Why do plants need surrounding fluid to always be hypotonic?

  -water can move in by osmosis and cells stay turgid
• What is active transport?

  movement of substances against a concentration gradient, across a partially permeable membrane, requiring energy.
• Examples of active transport?


  -plants absorbing mineral ions through the soil

  -sugar (glucose) absorbed out of gut into blood
• Ways an exchange surface area can be increased?

  -having a large surface area over which exchange can take place

  -having thin membrane or being thin to provide short diffusion path

  -efficient blood supply maintains steep concentration gradient

  -being ventilated maintains steep concentration gradient
• Adaptation of alveoli


  -enormous surface area

  -very rich blood supply
• Adaptation of the villi of small intestine

  -large surface area

  -short diffusion path

  -rich blood supply
• How are plants modified to have efficient gas exchange

  -Flat, thin leaves

  -presence of air space in leaf tissues

  -stomata
• Explain how osmosis helps to maintain the cytoplasm and plant and body cells at a specific concentration

  -if cells use up water in chemical reactions, cytoplasm becomes too concentrated, water moves into cells by osmosis

  -if cells make water during chemical reactions and cytoplasm becomes too dilute, water moves out of cells by osmosis
• Why is it important for cells of human body that solute concentration of fluid surrounding the cells is kept as constant as possible?

  -minimize changes in size and shape of cells

  -if solute concentration in cells outside the cells is more dilute water will move into cells by osmosis and cells will swell and burst

  -is solute concentration in cells outside the cell is more concentrated, water will move out and cells will shrivel and shrink
• Suggest and explain why osmosis is so important in the structural support system of plants

  -Plants rely on osmosis to support stems and leaves

  -Water moves into plant cells by osmosis

  -Vacuole swells and presses cytoplasm against plant cell walls

  -Turgor pressure reached when pressure is so great no more water can physically enter the cell

  -this makes cells hard and rigid, preventing wilting
• Explain how active transport works in a cell


  -Useful molecule binds to transport protein in cell membrane

  -Transport protein changes shape and moves useful molecule across membrane into cell

  -against the concentration gradient

  -Useful molecule is released, transport molecule returns to original position
• Explain how the surface area to volume ratio of an organism affects the way it exchanges materials with the environment

  -Affects how quickly organisms can exchange material with outside world

  -Smaller ratio means diffusion alone cannot provide sufficient gas and food molecules to cell and metabolic waste cannot be removed quickly enough