cell structure

• what are eukaryotic cells?

  animal and plant cells that have genetic material which form chromosomes enclosed in a nucleus
• what are prokaryotic cells?

  bacterial cells that have no nucleus - only a single loop of DNA and small rings of DNA called plasmids
• compare the sub-cellular structures between eukaryotic cells:

  BOTH: PLANT ONLY:

  -cell membrane -cell wall

  -cytoplasm -chloroplasts

  -nucleus -permanent vacuole

  -ribosomes

  -mitochondria
• what is the function of the cell membrane?

  to control the movement of substances in and out of a cell
• what is the function of the cell wall?

  made of cellulose which strengthens the cell
• what is the function of the nucleus?

  contain DNA and control all cellular activities
• what is the function of cytoplasm?

  contain chlorophyll to absorb light energy for photosynthesis (site of cellular reactions)
• what is the function of mitochondria?

  where energy is released for respiration
• what are the function of ribosomes?

  site of protein synthesis
• what is the function of a vacuole?

  contain cell sap which supports the cell, maintaining its turgidity
• what is cell differentiation?

  the process by which cells become specialised
• why is cell differentiation important?

  allows production of different tissues and organs that perform vital functions in the body
• describe the function of a sperm cell and its adaptations:

  FUNCTION: to fertilise an ovum

  ADAPTATIONS:

  -long tail to swim to the ovum and fertilise it

  -lots of mitochondria to release energy from respiration, which enables the sperm to swim
• describe the function of a red blood cell and its adaptations:

  FUNCTION: transport oxygen around the body

  ADAPTATIONS:

  -no nucleus so more room to carry oxygen

  -contains a red pigment called haemoglobin that binds to oxygen molecules

  -flat biconcave disc shape for an increased SA:V
• describe the function of a muscle cells and its adaptations:

  FUNCTION: contracts and relaxes to allow movement

  ADAPTATIONS:

  -contains protein fibres which can contract to make cells shorter

  -lots of mitochondria to release energy from respiration, allowing the muscles to contract
• describe the function of a nerve cell and its adaptations:

  FUNCTION: carry electrical impulses around the body

  ADAPTATIONS:

  -branched ending (dendrites) which make connections with other neurones or effectors to receive impulses

  -long axon allows electrical impulses to be transmitted to all over the body

  -myelin sheath insulates the axon and speeds up transmission of impulses along the nerve cell
• describe the function of a root hair cell and its adaptions:

  FUNCTION: absorb mineral ions and water from dilute soil

  ADAPTATIONS:

  -large SA/projection to speed up absorption of mineral ions and water from soil

  -lots of mitochondria to release energy from active transport from the soil
• describe the function of a xylem cell and its adaptations:

  FUNCTION: to transport mineral ions and water from the soil to the rest of the plant

  ADAPTATIONS:

  -made of dead cells with no end walls between them to provide a continuous route of water flow

  -thick walls stuffed with lignin to strengthen

  -one way transport only
• describe the function of a phloem cell and its adaptations:

  FUNCTION: transport dissolved sugars from the leaves to the rest of the plant

  ADAPTATIONS:

  -sieve plates let dissolved amino acids and sugars to be transported up and down the stem

  -substances are transported in both directions

  -companion cells provide energy needed for active transport of substances along the phloem
• describe the function of a palisade cell and its adaptations:

  FUNCTION: carries out photosynthesis in a leaf

  ADAPTATIONS:

  -lots of chloroplasts containing chlorophyll to absorb light energy

  -located at the top of the leaf's surface where it can absorb the most light energy
• define magnification:

  the number of times bigger an image appears compared to the actual size of the object
• define resolution:

  the smallest distance between two objects that can be distinguished
• how does a light microscope work?

  passes a beam of light through a specimen which travels through a lens allowing it to be observed
• what are the advantages of a light microscope? (4)

  -inexpensive

  -easier to use

  -portable

  -observe both dead and living organisms
• what is a disadvantage of light microscopes?

  -low resolution

  -low magnification
• how does an electron microscope work?

  uses a beam of electrons which are focused using magnets. the electrons hit a fluorescent screen which emits visible light producing an image
• what is an advantage of electron microscopes?

  greater magnification and resolution
• how have electron microscopes enabled scientists to develop their understanding of cells?

  -allow sub-cellular structures to be observed in detail

  -scientist can develop more accurate explanations about how a cells structure relates to its function
• what are the disadvantages of electron microscopes? (3)

  -expensive

  -large so less portable

  -only dead specimens can be viewed
• how is magnification calculated?

  image size/actual size