Biology Unit 2

• Nucleus - contains genetic material that comtrols the activities of the cell
• Cytoplasm - gel-like substance where most chemical reactions happen (contains enzymes)
• Cell membrane - holds the cell together and controls what goes in and out
• Mitochondria - where respiration reactions take place
• Ribosomes - where protreins are made in the cell

• Cell wall - supports and strengthens the cell (made of cellulose)
• Permanent vacuole - contains cell sap
• Chloroplasts - where photosynthesis occurs which makes food for the plant (contain chlorophyll)

- yeast is a single-celled organism (nucleus, cytoplasm, cell membrane, cell wall)

- bacterial cells have no nucleus (cytoplasm, cell wall, cell membrane, genetic material)

- diffusion is the spreading out of particles from an area of high concentration to an area of low concentration

- happens in solutions and gases

Cell membranes

• hold the cell together but let stuff in and out as well
• only small molecules can diffuse through them (e.g oxygen, glucose, amino acids, water)

Palisade leaf cells for photosynthesis - packed with chloroplasts at top of leaf, tall shape for larger surface down the side for absorbing CO2 from the air in the leaf, thin shape means lots can be packed in

Guard cells for opening and closing pores - kidney shape that opens and closes the stomata, lots of water makes it plump and open more so gases can be exchanged for photosynthesis, when short of water it goes flacid and closes up preventing water loss as vapour, thin outer walls and thick inner walls make the opening and closing work, sensitive to light so close at night

Red blood cells for carrying oxygen - concave shape creates big surface area to absorb oxygen, packed with haemoglobin (pigment that absorbs oxygen), no nucleus so more room for haemoglobin

Egg cells for reproduction - contains huge food reserves to feed embryo, membrane changes structure when a sperm fuses with it

Sperm cells for reproduction - long tail and streamlined head for swimming, mitochondria to provide energy needed, enzymes in head to digest through egg cell membrane

Cell             Tissue               Organ                Organ system

Muscular tissue - contracts to move what its attached to

Glandular tissue - makes and secretes chemicals like enzymes and hormones

Epithelial tissue - covers parts of the body (e.g inside of the gut)

Example - stomach:

• glandular tissue makes digestive juices to digest food
• muscular tissue moves the stomach wall to churn up food
• epithelial tissue coats the inside and outside of the stomach

Mesophyll tissue - where most photosynthesis occurs

Xylem and Phloem - transport water and minerals around the plant

Epidermal tissue - covers the whole plant

                                           sunlight

Carbon dioxide + water                         glucose + oxygen

                                         chlorophyll

Limiting factors:

• light (e.g at night)
• temperature (e.g winter)
• carbon dioxide (e.g if the others aren't limiting as there is a set concentration in the air and its not huge)

Creating artificial ideal conditions - farming:

• greenhouses trap heat
• heater to increase heat
• shades and ventilation to cool down when too hot
• artificial light
• paraffin heater as heats but also releases carbon dioxide as a by product

Respiration - uses glucose which releases energy to convert more glucose into other useful substances which can be used to build new cells and grow (some substances also need minerals from the soil as well)

Making cell walls - glucose is converted into cellulose for making cell walls

Making proteins - glucose is combined with nitrate ions to make amino acids which are made into proteins

Stored in seeds - glucose is turned into lipids and stored in seeds

Stored as starch - glucose it turned into starch and stored in roots, stems and leaves ready for use when photosynthesis isn't happening (it is insoluble)

Ways to study the distribution of an organism:

• measure how common an organism is in two sample areas (quadrats) and compare them
• study how the distribution changes across an area (e.g quadrats placed along a transects)

Mean = total number of organisms/number of quadrats

Mode = most common value

Median = middle number

Population size = mean * total area

Transects - mark out line and collect data along the line

**must think about reliability and validity

• biological catalysts
• a substance that increases the speed of a reaction, without being changed or used up in the reaction
• enzymes only catalyse one reaction as they have specific shapes
• substances are either split apart or joined together

- temperature and PH are essential and if they aren't the right conditions for the enzyme then it will be denatured

- digestive enzymes break down big molecules into smaller ones

Protease - breaks down proteins into amino acids (made in the stomach, pancreas and small intestine)

Lipase - breaks down lipids into glucose and fatty acids (made in the pancreas and small intestine)

Amylase - breaks down starch into sugars - e.g maltose (made in the salivary glands, pancreas and small intestine)

- bile neutralises the stomach acid and emulsifies fats

Salivary glands - produce amylase in saliva

Gullet - oesophagus

Liver - produces bile

Gall bladder - stores bile before it is released into the small intestine

Large intestine - where water is absorbed from food

Rectum - where the faeces are stored

Small intestine - produces protease, amylase and lipase, also where food is absorbed into the blood

Pancreas - produces protease, amylase and lipase and releases them into the small intestine

Stomach - produces protease (pepsin), pummels the food and produces hydrochloric acid to kill bacteria and give the right PH for protease to work

- respiration is the process of releasing energy from glucose which goes on in every cell

Aerobic respiration:

glucose + oxygen                         carbon dioxide + water + energy

Examples of what the energy released is used for:

• building larger molecules from smaller ones
• allowing muscles to contract in animals
• to regulate body temperature in mammals and birds
• to build sugars, nitrates and nutrients into amino acids in plants which can then be built into proteins

• muscle cells use oxygen to release energy from glucose
• an increase in activity causes a bigger demand in oxygen and glucose
• this is why you breathe faster and deeper and your heart rate increases to get more oxygen and glucose to your muscles and remove the carbon dioxide

- some glucose is stored as glycogen (each muscle has its own store) which during exercise is converted back into glucose to provide extra energy

Anaerobic respiration - glucose                 energy + lactic acid

• this method is painful and causes muscle fatigue, also not as much energy is released

Oxygen debt:

• having to 'repay' the oxygen that didn't get to your muscles in time because your lungs, heart and blood couldn't keep up with the demand
• you breathe hard after excercise to replace this oxygen and it removes the lactic acid in your muscles by oxidising it to harmless carbon dioxide

Biological detergents - usually contain proteases and lipases to break down stains on clothes (animal and plant matter), they also are more effective at working at lower temperatures so save on energy

Baby foods - the proteins are already partially digested so it is easier for the baby to digest it

Slimming foods and drinks - glucose syrup can be turned into fructose syrup using an isomerase enzyme, fructose syrup is sweeter so you need less of it

(carbohydrases turn starch syrup into sugar syrup)

Using enzymes in industry:

Advantages:

• they're specific so catalyse the reaction you want them to
• lower temperatures and pressures means less energy is used so the cost is lower
• they work for a long time so you can continually use them after purchase
• they are biodegradable so cause less environmental pollution

Using enzymes in industry

Disadvantages:

• some people can develop allergies to the enzymes
• enzymes are denatured easily so the conditions must be tightly controlled
• enzymes can be expensive to produce
• contamination of enzymes with other substances can affect the reaction

• DNA stands for deoxyribonucleic acid
• it is found in the nucleus in long molecules called chromosomes

Genes - a gene is a section of DNA that contains instructions to make a specific protein. Cells make proteins by stringing amino acids together in a specific order. Only 20 amino acids are used but they make up thousands of different proteins. DNA determines what proteins the cell produces, which determines what type of cell it is.

- DNA fingerprinting is a way of cutting up a person's DNA into small sections then seperating them.

- everyones DNA except twins and clones has a different pattern meaning you can tell people apart by comparing DNA samples

Forensic science - uses DNA from a crime scene and compares it with suspects to find the criminal

Paternity testing - DNA is used to see if a man is the father of a perticular child

• makes new cells for growth and repair

- mitosis is when a cell reproduces itself by splitting to form two identical offspring

• cell gets a signal to divide
• the DNA is duplicated
• the chromosomes line up and cell fibres pull them apart
• membranes form around the two sets of chromosomes (become the nuclei)
• the cytoplasm divides

- asexual reproduction uses mitosis

- meiosis produces cells that have half the number of normal chromosomes

• DNA is duplicated
• the pairs are pulled apart so each new cell has only one copy of the chromosome
• the arms of these chromosomes are then pulled apart to form four gametes wach with a single set of chromosomes in it

- gametes only have one copy of each chromosome

- meiosis involves two divisions

• undifferentiated cells are called stem cells
• human embryos contain stem cells which have the potential to turn into any kind of cell
• bone marrow also contains stem cells but they can only turn into certain types of cell

- stem cells may be able to cure many diseases

**some people are against stem cell research as embryos are a potential life

• All men have an X and Y chromosome, the Y part causes male characteristics
• All women have two X chromosomes, the ** combination causes female characteristics

Genetic diagrams:

• put the possible gametes of one parent down the side and the other parent along the top
• in the middle squares you fill in the letters from the top and side that line up from the square
• the pairs of letters in the middle show the possible combinations

- did genetic experiments with pea plants

- concluded that the tall plant gene was dominant over the dwarf plant gene

Important conclusions:

• characteristics in plants are determined by hereditary units
• hereditary units are passed on from both parents, one from each parent
• hereditary units can be dominant or recessive

**we now know that hereditary units are genes

• genetic diagrams show the possible genes of offspring
• alleles are different versions of the same gene
• homozygous - two alleles for a particular gene that are the same
• heterozygous - two alleles for a particular gene that are different
• if two alleles are different only one can determine the characteristic which is the dominant one
• for an organism to display a recessive characteristic, both its alleles must be recessive

- phenotype - the actual characteristic

- genotype - the alleles you have

Cystic fibrosis - genetic disorder of the cell membranes, resulting in the body producing a lot of thick sticky mucus in the air passages and pancreas

- the allele for it is recessive so both parents must be carriers or sufferers for the child to have a chance of having the disorder

Polydactyly - genetic disorder where a baby is born with extra fingers or toes

- the allele for it is dominant so if just one parent has it there is a 50% chance the child will be a sufferer

Embryos can be screened for genetic disorders:

Against - may come to a point everyone wants it to have the most 'desirable' child, the rejected embryos are destroyed, implies people with genetic problems are 'undesirable', its expensive

For - helps stop people suffering, there are laws to stop it going too far, in IVF most embryos are destroyed anyway so its just picking a heathy embryo, treating disorders costs the government lots

Gradual replacement by minerals - things like bones that don't decay easily when buried are eventually replaced by minerals as they decay forming a rock like substance shaped like the original part, the surrounding area also turns to rock but the fossil stays distinct and eventually someone digs it up

Casts and impressions - sometimes an organism is buried in something soft like clay which later hardens around it and the organism decays leaving a cast of the organism

Preservation in places where no decay occurs - in amber and tar pits there is no oxygen or moisture so decay microbes can't survive, in glaciers it is too cold for decay microbes to work, peat bogs are too acidic for decay microbes

Reasons a species may become extinct:

• the environment changes too quickly (e.g haitat destroyed)
• new predator kills them all
• a new disease kills them all
• they can't compete with another species for food
• a catastrophic event happens that kills them all
• a new species develops (speciation)

Isolation and natural selection lead to speciation:

• two populations of a same species
• physical barriers seperate the populations
• populations adapt to new environments
• development of a new species