cell biology

• a prokaryotic cell is a cell without a nucleus, their dna is often stored in plasmids or in loops: examples are bacteria.
• the cell wall is made of cellulose, and provides strength and support to the cell especially under pressure from osmosis.
• the vacuole contains cell sap and helps to keep the cells shape.
• chloroplasts are packed with chlorophyll and are the sites of photosynthesis.
• prokaryotes do not have chloroplasts, mitochondria or a nucleus.
• prokaryotes (0.1-5 micrometers) are smaller then eukaryotes (10-100 micrometers).
• centi- 0.01 of a meter

  milli- 0.001 of a meter

  micro- 0.000,001 of a meter

  nano- 0.000,000,001 of a meter
• The nucleus contains DNA coding for a particular protein needed to build new cells and is enclosed in a nucleur membrane.
• The cytoplasm is where chemical reactions occur, it contains enzymes and organelles are found in it.
• The cell membrane controls what enters and leaves the cell.
• The mitochondria is where respiration reactions occur, providing energy for the cell.
• Ribosomes are where protein synthesis occurs.
• a plant cell has a cell membrane, cell wall, vacuole, mitochondria, ribosomes, cytoplasm, chloroplasts and a nucleus
• bacteria divide by binary fission which is simple cell division: one bacterial cell splits into 2 identical cells, they carry out this process once every 20 minutes if they have enough nutrients and the temperature is suitable.
• mitosis cell cycle:

  1. DNA replicated to form 2 copies of each chromosome and internal structures are copied
  2. Mitosis: one set of chromosomes is pulled to each end of the cell and the nucleus divides
  3. The cytoplasm and cell membrane divide to form 2 identical cells
• functions of mitosis:

  • essential for growth and development of multicellular organisms
  • when an organism heals itself
  • during asexual reproduction
• objective lens: produces magnified image

  eyepiece lens: magnifies image and directs into the eye

  
• a culture medium contacts carbohydrates for energy, minerals, proteins and vitamins
• ways to grow microorganisms:

  1. nutrient broth solution- making a suspension of bacteria grow and mix with nutrient broth, stoppering the flask with cotton wool to prevent air contamination and shaking regularly to provide oxygen
  2. agar gel plate- hot sterilised agar jelly poured into petri dish, left to cool and set, inoculating loop dipped in microorganism solution and spread over agar evenly, lid taped on and incubated upside down
• why petri dishes and culture media must be sterilised with UV light:

  • to stop contamination by other organisms
  • organsims could compete for nutrients, space or be harmful
  • could produce new pathogen
• why inoculating loop must be sterilised by passing through flame:

  • kills unwanted organisms
• why lid of petri dish sealed with tape (not completely):

  • stops airborne microorganisms contaminating culture
  • not sealed all the way as harmful anaerobic bacteria could grow
• why petri dish should be stored upside down:

  • to prevent condensation from the lid landing on the agar surface and disrupting growth
• why culture should be incubated at 25 degrees:

  • to stop harmful bacteria to humans from growing, (37C their optimum temperature)
  • at lower temperatures colonies of bacteria may not be able to grow
• inhibition zone= clear area left when bacteria are killed
• Bacterial cells have a cytoplasm, cell membrane, cell wall (peptidoglycen), single circular strand of DNA and plasmids.
• diffusion is the spreading out of particles of any substance in solution or particles of a gas resulting in the net movement from an area of high concentration to an area of lower concentration
• what is the effect of concentration gradient on diffusion?

  the greater the difference in concentration, the faster the rate of diffusion- because more particles are randomly moving down the gradient than are moving against it.
• what is the effect of temperature on diffusion?

  the greater the temperature, the greater the movement of particles resulting in more collisions and therefore a faster rate of diffusion.
• what is the effect of the surface area of the membrane of diffusion?

  the greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion.
• single-celled organisms can use diffusion to transport molecules into their body from the air as they have a relatively large surface area to volume ratio
• the gills are where gas exchange takes place in fish:

  1. oxygenated water passes through mouth and over gills
  2. each gill has gill filaments which have gill lamellae upon them which is where diffusion of oxygen into the blood and carbon dioxide into the water takes place
  3. blood flows in one direction while water flows in the other
• osmosis: movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane.
• osmosis in animals:

  • if external solution is more dilute, it will move into animal cells causing them to burst.
  • on the other hand, if external solution is more concentrated, excess water will leave the cell causing it to shrivel
• osmosis in plants:

  • if external solution is more dilute, water will move into the cell and into the vacuole, causing it to swell and resulting in turgor (essential to keeping leaves and stems of plants rigid)
  • if less dilute, water will move out of the cell and they will become soft. eventually, the cell membrane will move away from cell wall and it will die
• active transport: movement of particles from an area where they are in lower concentration to an area where they are in higher concentration- against their concentration gradient
• active transport in root hairs:

  • take up water and mineral ions (for growth) from soil
  • mineral ions usually in higher concentrations in the cells so diffusion cannot take place
  • requires energy from respiration to work