biology

PLANT CELLS                                                                                                                                 Cell Membrane- separates contents of cell from surroundings (controls movement of oxygen, glucose and carbon dioxide).                                                                                                Cytoplasm- where chemical reactions take place (contains organelles)                                            Nucleus- organelle containing DNA (controls activities of cell)                                        Mitochondria- where respiration occurs                                                                            Chloroplasts- organelles containing chlorophyll (absorbs light energy)                                          Large Vacuole- space in cytoplasm filled with cell sap (helps support by keeping rigid)                Cell Wall- made of tough cellulose (supports/ keeps shape of cell)

ANIMAL CELLS                                                                                                                               Cell Membrane                                                                                                                       Cytoplasm                                                                                                                                 Nucleus                                                                                                                             Mitochondria

plant and animal cells can be studied in greater detail using light microscopes. 

BACTERIAL CELLS

Chromosomal DNA- giant loop of DNA (contains most of genetic material)

Plasmid DNA- small loops of DNA (extra information)

Flagella- movement

Cell Wall- supports cell

Due to changes in microscope technology we have been able to see cells with more clarity and detail by using the electron microscope. 

A gene is a section of a molecule of DNA and it codes for a specific protein

A DNA molecule:

• Two strands coiled to form a double helix
• strands linked by a series of complimentary base pairs linked by weak hydrogen bonds              adenine-thymine, cystosine-guanine

• Wilkins and Franklin working on X-Rays, Franklin took X-Ray of DNA
• Wilkins showed Watson and Crick X-Ray of DNA, they then discovered the DNA model 
• Franklin died 1958
• Wilkins, Watson and Crick awarded Nobel Prize 1962

HUMAN GENOME PROJECT

worked out sequence of the human genome- this helped develop:

• testing for genetic disorders
• finding causation genes of certain diseases (Alzheimers)
• new treatments/cures for disorders
• looking at changes in genome over time (evolution)
• personalised medicines

ADVANTAGES & DISADVANTAGES

• golden rice- makes beta-carotene (produces Vitamin A - helps in humans) / May crossbreed 
• human insulin- using GM bacteria / doesn't suit everyone
• herbicide-resistant crop plants- reduces amount of crop spraying / herbicide-resistant weeds & loss of biodiversity

MITOSIS

the production of two identical diploid daughter cells with identical sets of chromosomes as the parent cell.                                                                                                                                   occurs in:

• growth
• repair
• asexual reproduction

MEIOSIS

the production of four genetically different haploid gametes, each with half the number of chromosomes.

at fertilisation, haploid gametes combine to form a diplod zygote. 

Cloning is an example of asexual reproduction which produces identical copies

HOW TO CLONE A MAMMAL:

• remove diploid nucleus from body cell
• enucleate egg cell
• insert diploid nucleus into enucleated egg cell
• stimulate so it divides by mitosis
• implant into surrogate mammals

advantages- making gentically identical copy of organism with desirable characteristics, producing copies of cows engineered to produce human insulin in milk.

disadvantages- very few embryos develop successfully (ethical), grow old quickly and die at a young age. 

drawbacks- not possible to make a new animal from an arm/leg

stem cells in the embryo can differentiate into all other types of cells, but as the animal matures, they lose that ability.

adavantages, disadvantages and drawbacks of adult and embryonic stem cell research:

• treating leukaemian (bone marrow transplant).
• doesn't always work (body destroys the new cells if too different)
• cloning can solve this 
• could treat many more problems 
• could be used illegally to make human clones 
• reprogramming cells into stem cells (no ethical issues) not ready yet
• could turn into cancerous cells

the order of bases on a DNA strand decides the genetic code. they synthesise amino acids (of which there are 20) which create chains to form a particular protein (protein synthesis).

Transcription:

• hydrogen bonds break and DNA unzips
• complimentary mRNA strand produced in nucleus (Uracil instead of Thymine)

Translation:

• mRNA attached to ribosome 
• coding of codons in mRNA for specific amino acids
• tRNA transfers amino acids to the ribosome
• amino acids link to form polypeptides
• polypeptides become a protein

each protein has its own specific number and sequence of amino acids, this results in different shaped proteins with different functions (including enzymes).

Gene mutations change the DNA base sequence. these mutations can be harmful, beneficial (evolution) or neither

harmful-

• bacteria resistance to antibiotics (ones with mutation survive)

enzymes are biological catalysts

they catalyse chemical reactions inside and outside living cells including:

• DNA replication
• protein synthesis
• digestion

enzymes are highly specific for their substrate.

lock and key hypothesis:

• substrates fit into active sight neatly
• enzyme holds to make a bond
• creates product molecule

if there are changes in the shape of the active sight, the enzyme will denature

respiration is a process used by all living organims which releases energy in organic molecules

the human circulatory system facilitates respiration:

• Glucose + Oxygen diffuse from capillaries into respiring cells
• Carbon Dioxide diffuses from respiring cells into capillaries

diffusion is the movement of particles from an area of high concentration to an area of low concentration down a concentration gradient.

Aerobic Respiration

uses oxygen to release energy from glucose 

Glucose + Oxygen -->  Carbon Dioxide + Water

heart rate and breathing rate increase with exercise as blood supply to the muscles increases

cardiac output = stroke volume x heart rate

when doing vigorous exercise, muscle cells may not recieve sufficient amounts of oxygen for their energy requirements and therefore respire anaerobically 

anaerobic respiration releases less energy than aerobic respiration

glucose -> lactic acid (the energy from the glucose is released for use in the cell)

build up of lactic acid requires extra oxygen to break it down this is called (Excess Post-exercise Oxygen Consumption).

the heart and breathing rate remain high after exercise in order to get this extra oxygen

photosynthesis uses light energy to produce glucose:

carbon dioxide + water -> glucose + oxygen

leaves are adapted for photosynthesis:

• large surface area
• chlorophyll in chloroplasts to absorb light
• stomata for gas exchange (CO2, O2, H2O)

these three limiting factors can affect the rate of photosynthesis:

light intensity:                                 temperature:                                                           

CO2 concentration:

the loss of water vapour from leaves drives transpiration, the surface of roots have specialised root hair cells that reach out into the soil  (giving a large surface area).

the water enters the root hair cells by osmosis (the movement of water molecules from an area of high concentration to an area of low concentration down a concentration gradient through a semi-permeable membrane.

roots absorb nitrates and other mineral ions dissolved in soil water even if concentration is higher in the plant than in the soil. absorbing particles against a concentration gradient is called active transport and requires energy from respiration.

when the water and minerals have entered the root cells, the plants specialised tissue called xylem (long cells which have died to form hollow tubes) is used for transport. 

glucose made in leaves is converted into sucrose and transported to other parts of the plant using living phloem tissue.

when stomata are open, water can leave the leaf by diffusion, maintaining a concentration gradient (loss of water pulls up nutrients from roots). this is called transpiration.

there is a relationship between and environment and the animals that are able to live in that environment.

sampling can be used to look at a small portion of an area or population 

random sampling techniques:

• pooters
• sweep nets/pond nets
• pitfall traps
• quadrats 

environmental factors:

• light intensity
• temperature
• pH

the fossil record can be used as evidence for evolution, 

however there are gaps in the fossil record because:

• fossils don't always form
• haven't been found yet
• soft tissue decays

pentadactyl limb is also evidence for evolution it shows vertebrates all have a common ancestor:

• humerus
• radius 
• ulna
• carpals
• phalanges  

growth is an increase in size, length, mass and cell number, the data can be shown using percentile charts.

the cell division happens at the meristem.

cell division, elongation and differentiation contribute to the growth and development of a plant

cell divison and differentiation contribute to the growth of an animal

there are four different structures in blood including:

• red blood cells- 
  contain a red pigment called haemoglobin which combines reversably with oxygen
  haemoglobin + oxygen -> oxyhaemoglobin
  when blood passes through the lungs, it combines with oxygen and then transported to tissues around the body, where the oxygen is released
  it's shape is like a bionconcave disk to give it a higher surface area and no nucleus for room
• white blood cells-
  part of defence against disease, they can make antibodies (proteins) which bind to the microorganism and destroy them
  others surround and destroy any foreign cells in the body, they also have a nucleus
• plasma- 
  a yellow liquid which transports dissolved substances such as carbon dioxide, food substances and hormones
• platelets-
  tiny fragments of cells which make blood clot if you cut or damage your blood vessels. when the clot dries out, it forms a scab which also stops microorganisms getting into the body

a group of the same type of specialised cells forms a tissue, an organ contains several tissues working together to carry out a particular function eg. the heart

• there are four major blood vessels- pulmonary artery(to lungs), pulmonary vein(from lungs), aorta(carries blood to rest of body), vena cava(brings blood)
  
• left atrium and ventricle pumps oxygenated blood
• right atrium and ventricle pumps deoxygenated blood
• valves prevent backflow
• left ventricle has a thicker muscle wall than the right ventricle
  
  

the circulatory system transports substances around the body through blood vessels

• arteries carry blood away from the heart
• veins transport blood to the heart
• capillaries exchange materials with tissues by diffusion

• mouth- broken up (surface area for enzymes), bolus, saliva, swallow
• oesophagus- muscular tube, muscles contract in waves (peristalsis)
• stomach- muscular bag, makes acid/enzymes, churns food up by peristalsis, paste
• small intestine- long, muscular tube, peristalsis, insoluble into soluble, absorbed by villi
• pancreas- makes digestive enzymes, releases into first part of small intestine
• large intestine- wide, thin walled, undigested food, water diffuses into blood
• anus- undigested food passed out of the body
• liver- once in blood, taken to liver, some broken down, some built up, also makes bile
• gall bladder- stores bile made by liver, releases into small intestine when needed

Carbohydrates:
the simplest carbohydrates are sugars, which can be built up into starch
carbohydrases break down carbohydrates, eg. amylase breaks down starch into sugars
amylase is present in the saliva and the small intestine

Proteins:
proteases break down proteins into shorter chains and then amino acids
pepsin is made in the stomach and works best in acidic conditions (pH2-3)
the contents of the small intestine are alkaline so proteases work best at about pH 8 

Fats:
lipases are enzymes that digest fats, they break them down into fatty acids and glycerol

Bile:
fat & water don't mix, form globules in the watery digestive juices (small surface area compared to volume) bile breaks them down forming emulsion the bile emulsifies fat, meaning lipase can break it down more easily
bile from the gall bladder is alkaline (neutralises acid in stomach) & slightly alkaline environment for protease enzymes of the small intestine to work in

digested food passes into the blood by diffusion, the larger the surface area, the more diffusion

the small intestine has millions of finger like folds (villi) giving a large surface area

each villus has a large network of capillaries, lower conc. of food molecules in the blood than the small intestine, creating a steep concentration gradient

single layer of cells between small intestine and blood vessels in villi, short distance for diffusion.

probiotics contain bifidobacteria and lactic acid bacteria lactobacillus- not proven that it helps to improve your digestive system

plant stanol esters are oily substances found in plants, they can stop the small intestine absorbing cholesterol- clear evidence that they have an effect

prebiotics are substances that the body can't digest, they act as food for the 'beneficial' bacteria in the gut/encourage their growth 
tomatoes, bananas, onions and asparagus all contain oligosaccharides
the evidence is growing that they can increase the beneficial bacteria in your gut and maintain good health