cell structure

• Plant and animal cells (eukaryotic cells) have:

  • Cell membrane
  • Cytoplasm
  • Genetic material enclosed in a nucleus
• Bacterial cells (prokaryotic cells) are much smaller in comparison to eukaryotic cells
• Bacterial cells have:

  • Cytoplasm
  • Cell membrane
  • Cell wall surrounding the cell membrane
  • Genetic material not enclosed in a nucleus
  • Single DNA loop
  • One or more small rings of DNA called plasmids
• • animal cells are between 0.01 mm – 0.05 mm
  • plant cells are between 0.01 mm – 0.10 mm
• Parts found in most animal cells:

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• In addition to the parts found in animal cells, plant cells often have:

  • Chloroplasts
  • A permanent vacuole filled with cell sap
• Plant and algal cells have a cell wall made of cellulose, which strengthens the cell
• cytoplasm is a jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the chemical reactions happen.
• nucleus contains genetic material, including DNA, which controls the cell’s activities.
• cell membrane is a selectively permeable membrane that controls the movement of substances into and out of the cell
• mitochondria contains the enzymes for respiration, and where most energy is released in respiration.
• ribosomes are tiny structures where protein synthesis occurs
• chloroplast organelles are found in plant cells and contain chlorophyll, which absorbs light energy
• cell wall is made of cellulose and is found in plant cells
• permanent vacuole is a large vacuole that contains cell sap and is found in plant cells
• use a light microscope to observe, draw and label a selection of plant and animal cells. A magnification scale must be included.
• Steps to prepare a microscope slide:

  • Place a drop of water in the middle of the slide using a pipette
  • Peel a small layer of tissue sample and place it into the water droplet on the slide using tweezers
  • Add a drop of stain solution (e.g. Iodine Solution) to help stain the tissues for better visibility under the microscope
  • Place a coverslip on top slowly by tilting it to avoid air bubbles that could obstruct the view of the tissues
• Steps to view the specimen under the microscope:

  • Clip the prepared slide onto the stage of the microscope
  • Adjust the microscope settings for a clear view:
  • Use different powered lenses with varying levels of magnification on the Objective Lens
  • Use the Coarse Adjustment Knob to move the stage up and down, positioning it just below the objective lens
  • Use the Fine Adjustment Knob to get a clear, focused image by turning it while looking into the eyepiece
• Steps to prepare and view tissue sample under a microscope:

  • Prepare tissue sample and place it on a microscope slide
  • Place a clear ruler with mm readings on top of the slide and clip both the slide and ruler on the microscope stage
  • Select the objective lens with 100x magnification
  • Use the Coarse and Fine Adjustment Knobs to get a clear and focused image
• Procedure to measure the length of an individual cell:

  • Adjust the ruler so that the cells are lined up between the 1mm marks
  • Count the number of cells within the 1mm marks
  • Calculate the length of an individual cell by dividing 1mm by the number of cells counted
• sperms cells: specialised to carry male DNA to the egg cell for successful reproduction
• sperm cells are adapted as they have a long tail to help them swim and a head with lots of mitochondria which supply the energy needed for the sperm to move. the acrosome has digestive enzymes which break down the outer layer of the egg cell.
• nerve cells are specialised to carry electrical impulses around the body.
• 1. the nerve cell is adapted as it has a long axon which enables impulses to be carried along long distances
  2. lots of extentions from the cell body extensions means branched connections can form with other nerve cells
  3. many mitochondria to supply energy to make neurotransmitters
• muscle cells are specialised for contraction and movement,

  1. they have lots of mitochondria for energy for chemical reactions
  2. special protein that slides over each other making the fibres contract
  3. store glycogen which can be broken down and used for respiration by the mitochondria
• root hair cells are specialised to take up water by osmosis and minerals from the soil by active transport

  1. have a large surface area so more water can move in
  2. large permanent vacuole affects the speed of movement of water from soil to cell
  3. mitochondria to provide energy from respiration for active transport of mineral ions into root hair cell
• xylem cells are specialised to transport water and mineral ions from the roots to the leaves

  1. they lose their end walls so the xylem forms a continuous hollow tube
  2. strengthed by lignin
• phloem cells are specialised to carry the products of photosynthesis to all parts of the plants

  1. made up of columns of living cells
  2. the end walls of pholem cells contain small holes to allow food products to move up and down the pholem vessels
• Differentiated cells are important in a multicellular organism because they are able to perform a specialised function in the body.
• Most types of animal cell differentiate at an early stage.
• Many types of plant cells retain the ability to differentiate throughout life
• In mature animals, cell division is mainly restricted to repair and replacement. 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.
• Cells can be seen with microscopes. 
• Light microscopes were created first. Light microscopes have a magnification power of up to x2000. 

  • use the beams of light and lenses in order to magnify a living object to create an image. 
  • They are cheap and portable 
  • can be used to see cells and large organelles, or sub-cellular structures, such as nuclei.
• • Electron microscopes changed the field of biology. 
  • Electron microscopes have a much higher magnifying power than light microscopes, and so could be used to see more sub-cellular structures, improving our understanding of biology.
• An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.
• $magnification$= size of image / size of real object
• Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.
• Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate.
• Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.