Cell Biology

• Animal and plant cells are eukaryotic cells, bacteria are prokaryotic cells
• Cell membrane: controls things coming in and out

  Nucleus: contains DNA, controls cell activity

  Cytoplasm: where chemical reactions happen

  Mitochondria: releases energy for cell to function through respiration

  Ribosome: where proteins are made
• Cell wall: strengthens cell structure, made of cellulose

  Vacuole: has cell sap (sugars, etc)

  Chloroplasts: absorbs light for photosynthesis
• Bacteria (smaller)

  Plasmids: extra genes, antibiotic resistant

  Flagella: propels cell to move

  No nucleus: rings of DNA
• Light microscope:

  • easy to use ✅
  • limited resolution❌

  *lenses in microscope spread out light rays to make zoomed in image

  
• Electron microscope:

  • better resolution ✅
  • expensive, hard to use ❌

  *uses beams of electrons with short wavelengths to pick up electron patterns
• Magnification: how many times bigger an image is to an object

  Resolution: measure of how detailed an image is

  I = AxM

  
• Cell cycle: new cells needed for growth, repair & development

  • Interphase - cell grows, organelles grow & increase in number, DNA is replicated to form 2 copies of each chromosome in an X shape
  • Mitosis - chromosomes line up at equator of cell and cell fibres pull each chromosome out the X shape to each of the cell‘s poles
  • Cytokinesis - cell splits, 2 identical daughter cells form
• Binary fission: cell division and reproduction

  • bacteria grows and replicates organelles, DNA rings move to opposite sides, plasmids move randomly so one gets more than other
  • cell wall grows in the middle

  This is a fast process, unless it’s not warm, moist, etc
• Stem cells: divide via mitosis, can differentiate into specialised cells, can be used to treat diseases

  EMBRYONIC STEM CELLS: differentiate to anything, gone once born (ethical issues due to coming from embryo)

  ADULT STEM CELLS: can’t differentiate into everything, bone marrow has stem cells to make blood cells, don’t form new tissue
• Plant stem cells found in meristem (tips of shoots and roots), differentiate into palisade cells, phloem cells, etc

  *stay for life
• PRACTICAL 1: Microscopes

  • place slide onto stage of microscope, use clips to hold slide in place
  • select lowest power objective lens
  • turn coarse focusing dial until lens almost touches slide and look from side
  • look down eyepiece, move fine focusing dial until cells are clear
• PRACTICAL 2: CULTURING BACTERIA

  • use aseptic techniques - sterilise inoculating loop with flame
  • dip loop into bacteria solution, lift Petri dish lid slightly and make zig zag streaks on agar
  • place filter paper disks into different antibiotic solutions and place them in each colony on agar plate
  • secure lid and incubate at 25C to reduce harmful pathogen growth
• Stem cells in medicine:

  Embryonic stem cells are extracted from embryo, grown in lab, stimulated to differentiate into specialised cell, injected into patient

  (limited supply, rejection as identified as foreign)

  Adult stem cells won’t cause rejection but only turn into blood cells

  RISKS: virus transmission, tumour development (cells divide out of control)
• Sperm cells

  • Send genetic material to an egg to fertilise it
  • Half of genetic material (full genetic material once fused with egg)
  • Flagellum (easier swimming to egg)
  • Lots of mitochondria (energy for swimming)
• Nerve cells

  • Send electrical messages to body
  • Axon (carries electrical message from one part of body to other)
  • Dendrites (increased surface area to connect easier to others)
• Muscle cells

  • Contract
  • Mitochondria (make energy)
  • Ribosomes (make proteins controlling length)
• Root hair cells

  • Increase surface area on root to absorb water + minerals effectively
  • No chloroplasts (underground)
• PLANT SPECIALISED CELLS:

  • xylem cells carry water (ADAPTATIONS: thick walls made of lignin=support of plant , no organelles=easier for water to flow
  • phloem cells carry sugars (ADAPTATIONS: companion cells provide energy)
• Diffusion: net movement of particles from an area of high concentration to an area of low concentration

  passive process=no energy needed

  water and glucose diffuse through partially permeable membrane

  
  

  EG: alveoli, lungs, fish gills, stomata
• FACTORS AFFECTING DIFFUSION:

  • higher concentration gradient = faster diffusion
  • higher temperature = faster diffusion, more energy for particles to move
  • higher surface area = faster diffusion
• Osmosis: water diffusion

  (area of less solute to higher solute)

  
  

  EG: water enters root hair cells via osmosis and moves via xylem cells
• Active transport: movement of particles against concentration gradient (low to high)

  energy needed from cellular respiration

  EG: root hair cells mineral ions get absorbed to soil (area of low concentration turns to area of high concentration)
• SURFACE AREA TO VOLUME RATIO:

  • as organisms get larger, sa:v ratio decreases (less surface area compared to ratio)
  • HIGH sa:v ratio can rely on diffusion across surface
  • LOW sa:v ratio can’t rely on diffusion (eg: human lungs have alveoli to increase surface area inside body)
  • as organisms get bigger, diffusion distances increase = unreliable slower diffusion: transport systems like circulatory are needed
• Palisade cell: absorbs light for photosynthesis

  • lots of chloroplasts on top surface for efficient photosynthesis
• Chromosomes contain lots of genes made of DNA molecules
• ✅Plant meristem can be used to clone nearly extinct plants

  ❌Genetically identical clones lead to risk of being destroyed by genetic defect
• Therapeutic cloning:

  • cells from patient‘s body are used to make cloned embryo of themselves
  • stem cells from embryo can be used to grow new tissue
  • no rejection as the cells come from the same person
• Cells in HYPOTONIC solution: water moves into cell, cell expands and bursts (plant cell’s cell wall prevents bursting and becomes turgid)

  Cells in HYPERTONIC solution: if cell has higher water concentration than solution, water moves out and cell shrinks

  Cells in ISOTONIC solution: if cell and solution have same concentration, there’s no net movement
• Respiration: a reaction transferring energy from glucose
• Metabolism: all chemical processes occurring within an organism to maintain life using energy

  EG: forming large molecules from smaller ones, muscular contraction to move, maintaining a body temperature
• Aerobic respiration is the most efficient way to transfer energy from glucose

  (needs oxygen and occurs in mitochondria)
• Aerobic respiration equation

  glucose + oxygen → carbon dioxide + water

  (reverse of photosynthesis equation)
• Anaerobic respiration is only used when we have to (eg: can’t get enough oxygen due to sprinting)

  ❌ incomplete glucose breakdown (no oxygen to oxidise it, therefore not unlocking all energy)

  ❌ lactic acid builds up and has to be removed later
• Anaerobic respiration in plants and yeast (fermentation)

  glucose → ethanol + carbon dioxide

  • pockets of air from carbon dioxide in bread to make it fluffier
  • ethanol used for beer and wine
• Anaerobic respiration equation

  glucose → lactic acid
• Exercise

  more cellular respiration needed

  • more muscular contraction, lots of energy needed

  Need more oxygen

  • rate of breathing increases (muscles around lungs need more energy)
  • body needs to pump oxygen faster, heart rate increases (need more energy)

  [this increased effort allows enough oxygen to enter]
• Sprinting (anaerobic)

  lactic acid builds up in tissues and creates a burning sensation and damages cells if left

  • to get rid of it, lactic acid is carried by the blood from the muscles to the liver where it reacts with oxygen to turn to glucose
  • this reaction with oxygen creates an oxygen debt (which is why it’s hard to breath after excessive sprinting)
• Exothermic reaction


  Where energy is GIVEN OUT to the surroundings
• Endothermic 


  When energy is TAKEN FROM the surroundings