1 - Cell Biology

• • Eukaryotes: contain their genetic material (DNA) enclosed in  a nucleus (animals & plants)
• Prokaryotes: the genetic material (DNA) is not  enclose within a nucleus- it is within a single loop  of DNA, they are also much smaller than eukaryotic cells
• animals cells contain: cell membranes, cytoplasms, nucleus, mitochondria, and ribosomes
• plant cells contain: cell membrane, cytoplasms, nucleus, mitochondria, ribosomes, chloroplast vacuole and cellwall
• Conversion Scale

  km → m (x1000)

  m → cm (x10)

  mm → µm (x1000)

  µm → nm (x1000)
• Every order of magnitude is 10x greater than the one before. Eg: 10, one zero= one order of magnitude

  •  100x, two zeroes= two order of magnitude
• Animals Cells:

  1. Nucleus: to enclose the genetic material 
  2. Cytoplasm: water solution where chemical reactions take place (eg; first stage of respiration)
  3. Cell membrane: controls the molecules that can enter and leave the cell
  4. Mitochondria: producing energy needed for the cell to survive and function and contains enzymes for cellular respiration also where aerobic respiration takes place 
  5. Ribosomes: are the site of protein synthesis
• • Plant cells have a regular shape
  • Packed full of green structures 

  Functions: 3 structures which animal cells do not

  1. Chloroplasts: contain chlorophyll and are the sites of photosynthesis  
  2. Cell Wall: made from cellulose, strengthens the cell 
  3. Permanent Vacuole: filled with fluids called cell sap. This helps give the plant cell its shape.
• • Most animal cells are specialised; they have adaptations which help them carry out their particular function. When they become specialised they are called differentiated
• Sperm Cells Adaption:

  • The job of a sperm cell is to join with an ovum (egg cell) to go through the process of fertilisation- during fertilisation the genetic info of the ovum and sperm combine 
  • Sperm cells contain their genetic info in the nucleus, but they only contain half the into of a normal adult cell 

  Their adaption: 

  • Long Tails: allows them to swim to the ovum, also streamlined to make this easier.
  • Filled with mitochondria: Provide energy needed for swimming 
  • Enzymes: allow them to digest their way through the outer layer of the ovum
• Nerve cells Adaption: 

  • The job is to send out electrical impulses around the body 

  Their adaption: 

  • The Axon: carried the electrical impulses from one body part to another
  • Dendrites: increase the surface area so that the nerve cells can connect more easily 
  • Synapses: at the end of the axon. Are junctions which allow the impulse pass from one nerve cell to another 
  • Myelin:  insulates the axon and speeds up the transmission of the nerve impulses

  
• Muscle cells:

  • Can contract (get shorter)
  • They work together to form muscle tissue  

  Their adaption: 

  • Protein fibres: change their lengths, when a muscle cell contracts, these protein fibres shorten, decreasing the length of the cell 

  Mitochondria: to provide energy for muscle contraction
• Adaptations of the alveoli:

  • Large surface area - alveoli are present in the lungs with a shape that increases surface area.
  • Thin walls - walls are one cell thick providing gases with a short diffusion distance.
  • Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.
  • Good blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.
  • Permeable walls - allow gases to pass through.
• Root Hair Cells:

  • Increases the surface area of the root so it can absorb water and 

  dissolved minerals more effectively 

  • Do not contain chloroplasts because they’re underground

  (can't carry out photosynthesis- don’t need to)

  • Permanent vacuole – increases the speed of osmosis.
  • Long projections that increase the surface area that the plant can use to absorb water and minerals.

  
• Xylem Cells:

  • Xylems are found in the plant stem. They form long tubes
  • They carry water and dissolved minerals from the roots to the leaves 
  • Thick Walls: containing lignin- provides support to the plant, BUT because the cells are sealed with lignin
  • The end walls between the cells have broken down- this means that the cell now forms a long tube so water and dissolved minerals can flow easily 
  • No internal structure; makes it easier for things to flow through 

  
• Phloem Cells:

  • Phloem tubes carry dissolved sugars up and down the plant- consist of two types of cells 

  Phloem Vessel cells:

  • they have no nucleus and only limited cytoplasm, the end walls of the vessel cells have pores called sieve plates- both features allow dissolved sugars to move through the cell interior 

  Companion Cell

  • Each phloem vessel cell has a companion cell connector by pores- mitochondria in the companion cell provide energy to the phloem vessel cell 

  
• Preparing the slide: 

  1. Place slide on the stage and use clips to hold them in place
  2.  Select the lowest power objective lens (eg: 4x), you need to position the objective lens so it almost touches the microscope slide- turn the coarse focusing dial (look at the microscope from the side as you adjust- risk of damaging slide if you look through eyepiece.)
  3. Stop turning dial when lens almost touches slide
  4. Turn the coarse focusing dial: increases the distance between the objective lens and slide- do this until the cells come into focus then adjust fine focusing dial- to make cells clear

  
• Preparing A Stage:

  • Where you place the microscope slide, it has clips to hold them in place  
  • Below the stage is the lamp, the light from the lamp passes through the microscope slide 
  • Some microscopes have a mirror beneath the stage which reflect light up through the slide

  Lenses

  • Three different objective lenses with 3 different magnifications (eg: 4x, 10x, 40x), the eyepiece lens has a magnification of 10x 
• • Microscopes allow us to magnify 
  • Light microscopes have a limited magnification (can’t see details) and limited resolution (no fine detail) BUT they’re cheaper and handheld 
  • Electron microscopes have greater magnification and resolution BUT they’re expensive 
• magnification = image size / actual size

  
• Chromosomes

  • In the nucleus we find chromosomes which are made of molecule DNA
  • Body cells contain two of each chromosome, they are paired, they contain 23 pairs and they carry a large number of genes
  •  Cells divide through the cell cycle
• Cell Cycle 

  1. DNA replicated to form two copies of each chromosome, the cell also grows and copies its internal structures (eg: ribosomes and mitochondria)  
  2. Mitosis takes place - 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 two identical cells
• Functions of mitosis

  1. Essential for growth and development of multicellular organism (plants and animals)
  2. Takes place when an organism repairs itself (eg: when a broken bone heals)
  3. Happens during asexual reproduction 
• Stem Cells: an undifferentiated cell that can give rise to more cells of the same type and can differentiate to form other types of cells
• Embryonic Stem Cells 

  • Sperm joins with ovum and goes through fertilisation, the fertilised ovum undergoes mitosis and forms a ball of cells called an embryo  
  • Overtime it keeps going through mitosis and changes to begin specialised cells (nerve & muscle cells)- this the process of differentiation  
  • Cells in the early embryo have no differentiation, any of these cells are capable of differentiation into any type of body cell 
• Adult Stem Cells - limited  

  • Stem cell in bone marrow differentiation to form cells we find in blood (platelets, white/red blood cells) 

  Bone Marrow Transplant 

  • Leukaemia is cancer of the bone marrow 
  • To treat this the existing bone marrow is destroyed using radiation and the patient then receives transplant of bone marrow from a donor 
  •  The stem cells in the bone marrow now divide and form new bone marrow, they also differentiate and form new blood cells 
• Problems with bone marrow transplant: 

  1. Donor has to be compatible with the patience. otherwise the white blood cells produced by the donated bone marrow could attack the patient's body 
  2. Risk of viruses passed from donor to patient 
• Therapeutic cloning: 

  • An embryo is produced with the same genes as the patient, stems from the embryo can be transplanted into the patient without being rejected by the patient's immune system 
  • Once inside the stem cell can differentiate to replace cells which have stopped working. 
  • Can be used for diabetes or paralysis 
  • Some people have ethical or religious objections against this procedure 
• Plant Stem Cells 

  • Roots and buds contain meristem tissue- they can differentiate into any type of plant tissue at any point in the life of a plant  
  • Can produce clones of the plants quickly and cheaply- stop rare plants from going extinct or producing clones crop plants for farmers
• Diffusion: the spreading out of particles resulting in net movement from an area of higher concentration to an area of lower concentration
• Cell Diffusion

  • Cells need oxygen for respiration which is carried out by mitochondria, cells are surrounded by a high concentration of oxygen. 
  • Oxygen molecules move into the cell by diffusion, the oxygen is used to generate energy in respiration and this produces the waste gas carbon dioxide. This means there's a higher concentration of CO2 inside than outside, and through diffusion it moves out of the cell 
  • Urea is a waste product produced inside cells it diffuses out cells into the blood plasma and is excreted by the kidneys 
• Factors that affect rate of diffusion

  1. Concentration gradient (difference in concentration)- The greater the concentration gradient, the faster diffusion takes place 
  2. Temperature- higher the temp the greater the rate of diffusion

  • This is because the particles have more kinetic energy and are moving faster 

  1. Surface Area of the membrane- larger surface area, greater the rate of diffusion 
• total surface area = height x width x amount of sides

  volume = height x width x length

  SA:Vol (surface area / vol)

  
• Fish- Gill Adaptations 

  • oxygen rich water passes into the mouth and flows overs gills where the oxygen is transported into the bloodstream 
  • Gills are covered in fine filaments: where gases pass in and out the blood 
  • Deoxygenated blood passes into filament. Oxygen diffuses from the water into the blood. Oxygenated blood returns to the body. 
  • filaments give the gills a large surface area, also have a thin membrane to provide a short diffusion pathway 
  • filaments have an efficient blood supply to take oxygenated blood away. This ensures that the concentration gradient is always high 
• • Osmosis: is the diffusion of water molecules from a dilute solution to a more concentrated solution across a partially permeable membrane
  • Dilute solutions: have a high concentration of water
  • Concentration solutions: contain a lower concentration of water 
  • Partially permeable membranes allow some molecules to pass through
• Animal Cells: 

  1. Cytoplasm of cells- contains a relatively low concentration of water, if you place it in water then osmosis will take place
  2. Water will move from outside the cell to inside the cell, the water moving in will cause the cell to expand maybe even burst
  3. If you place the cell in a very concentrated solution, then water will move out and the cell will shrink
• Plant Cells: 

  1. If you place a plant cell in water, then water will move into the cell by osmosis and the cell will expand- the cell wall prevents from bursting and instead becomes swollen- this is called turgid
  2. If placed in concentrated solution, then water moves out the cell and it shrinks. This means the cell has become flaccid
• Required Practical: Effects of Osmosis on Plant Tissue

  Method 

  1. Add 10cm3 of distilled water (contains no dissolved substance- which could affect rate of osmosis) to a test tube 
  2. Then repeat sugar concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 molar sugar solution 
  3. Leave for your chosen amount of time 
  4. Remove the potato and roll them on paper towel to remove surface moisture (not forcing water out of the cell
  5. Measure length and mass
• Required Practical : Effects of Osmosis on Plant Tissue

  Preparation:

  1. Peel the potato, use a cork borer to produce cylinders of potato- this makes sure that the all have the same diameter 
  2. Use a scalpel to trim the cylinders to the same length
  3. Measure length and mass
• Percentage change= (change in value / original value) x 100