B3a: Molecules Of Life Aerobic respiration happens inside the mitochondria

The nucleus contains the mitochondria DNA is shaped as a double helix and controls

the production of proteins in a cell The bases C + G and A + T pair up, this is

called complimentary base pairing DNA replicates by unzipping the two strands ,

DNA bases in the nucleus then pair up to form 2 new strands

B3a: Molecules Of Life Making proteins is called protein synthesis- it happens in the cytoplasm

A protein is made of a long strand of amino acids

If you are short of amino acids, your liver can change one type into another- this is called transamination

The genetic code (the sequence of bases) determines the order that the amino acids should join and therefore the type of protein made

DNA fingerprinting or profiling means putting DNA on a gel and comparing the lines on the gel to see if they are in the same place e.g. on a crime suspect and the DNA found at the scene of the crime

B3a: Molecules Of Life Enzymes are proteins that speed up reactions

e.g. the enzyme amylase turns starch maltose

Starch is the substrate, maltose is the product Each enzyme is specific to one type of

substrate The enzyme has an active site where the

substrate binds with it Enzymes have an optimum temperature where

they react best If the temperature gets too high or the pH too

extreme, enzymes are denatured which means they change shape and can’t fit the substrate. The reaction slows down then stops

B3b: Diffusion The way that perfume spreads is called diffusion

A substance diffuses down a concentration gradient from a region of high concentration to a region of low concentration

Diffusion is faster if the distance is shorter, there is a big concentration gradient (difference) or a big surface area

The alveoli in the lungs are efficient at diffusion due to the above factors e.g. thin alveolus wall, steep concentration gradient between air and blood, big surface area

B3b: Diffusion The small intestine is long so plenty of time for diffusion, has villi and microvilli to increase the surface area

The placenta is thin, and diffuses oxygen, glucose and amino acids into the fetus, and urea and carbon dioxide out

Transmitter substances diffuse across a synapse

Plant leaves have a large surface area, are thin and the stomata on the lower surface allow gas exchange with the air

Transpiration is the word for water evaporating out of a leaf

B3c Keep It Moving Red blood cells are biconcave which gives them a large surface area

Haemoglobin in the red blood cells combines with oxygen in the lungs to form oxyhaemoglobin

White blood cells defend the body against disease by phagocytosis which means engulfing bacteria and viruses (pathogens)

Blood plasma contains nutrients like glucose and transports hormones, antibodies, water and waste products

Platelets clot the blood forming a scab for protection

B3c Keep It Moving Arteries have thick, elastic walls Capillaries have thin, permeable walls for

exchange Veins have thin walls with a large hole or

‘lumen’ Veins contain valves so the blood can only

flow one way A double circulatory system means that blood

visits the heart twice, once to be pushed around the body and once to be pushed to the lungs

Cholesterol is needed in the body to make cell membranes, too much cholesterol can build up as plaques on artery walls causing a blood clot

Damaged heart valves can be replaced with metal ones but anti clotting drugs are needed

A pacemaker sets the pace of the heart, it needs a constant power supply

Hearts can be transplanted, but you need immunosuppressant drugs to stop your immune system attacking it

B3d: Divide and Rule Multicellular means many cells- this is good as we have cell differentiation- each cell has a different job

Big animals have a small surface area to volume ratio, so it is hard for them to cool down- small animals have a big surface area to volume ratio

Human cells have two sets of 23 homologous chromosomes

A cell with two sets of chromosomes is called a diploid cell

B3d: Divide and Rule Mitosis means cell division, each division produces identical cells with a full set of chromosomes

Meiosis produces cells with half the number of chromosomes (haploid) these cells make sex cells (gametes)

Meiosis creates a lot of variation in sperm and egg cells

When two sex cells or gametes fuse together they create a zygote

B3e: Growing Up Plant cells have chloroplasts, a vacuole and a cell wall- this makes them different from animal cells

People stop growing in height at about 20 years old- some plants can grow for their whole lives

We get bigger by making more cells- plants get bigger mostly by enlarging their cells

Plants also grow by dividing their cells in special regions at the tips of shoots and roots

B3e: Growing Up Stem cells are able to divide and create specialised cells like nerve and muscle cells

Nerve and muscle cells are said to be differentiated- specialised for a particular function

You can find stem cells in embryos, and use them to help repair other parts of your body

People think stem cell science is unethical as you must take stem cells from fertilised eggs

Growth in humans is summarised as: infancy 0-2, childhood 3-11, adolescence 11-17, maturity and old age 18 +

The gestation period is the name given to the length of time in the uterus before birth- 9 months for humans

B3f: Plant Hormones A hormone is a chemical produced in one part

of the body that has an effect on the other Plant hormones: control growth of shoots and

roots, flowering and fruit ripening Positive phototropism is a plant growing

towards the light, negative phototropism is a plant growing away from the light e.g. roots

Auxins are hormones controlling growth towards light- they make plant cells in a shoot get longer on their shaded side by taking in water by osmosis- this makes them bend over towards the light

Coleoptiles are the tip of the shoot where auxin is made

B3f: Plant Hormones Positive geotropism is plants growing in the direction of gravity e.g. roots, negative geotropism is plants growing against gravity e.g. shoots

Plant hormones are used in agriculture Selective weedkillers kill some weeds and not

others, they contain auxin and make the plants grow so much they die

Rooting powder contains auxins and makes the roots of cuttings grow more quickly

Hormones can also be used to ripen or not ripen fruit depending on what you want e.g. transport time etc

Plants that are dormant (resting) in the winter can be sprayed with hormones to make them grow

Seeds are given a hormone called gibberellin to make them germinate and start growing

B3g: New Genes For Old A mutation is a sudden and unpredictable change in an organisms genes

Selective breeding means picking the best animals and making them breed to get the best offspring

Sometimes the best animals e.g. cows with most milk, also have a problem e.g. weak bones- you end up reducing the gene pool so that most cows have a lot of milk but weak bones etc.

Inbreeding means breeding two closely related animals- they may end up having the same genes and genetic illnesses. It also reduces the gene pool

B3g: New Genes For Old Reducing the gene pool means that there are less alleles e.g. breeding everyone together with brown eyes would mean the loss of blue eye alleles in the human population- once they are gone, you can’t get them back

We can now also put new genes into an organism- called gene technology, genetic engineering or genetic modification (GM)

The gene for insulin was put into bacteria and now they produce insulin for diabetics

Genes are put into crops to make them resistant to disease

B3g: New Genes For Old Genetic engineering = Select the characteristics isolate the gene

make copies of the gene insert the gene into an organism

Advantages : crops can be made with new features, like rice with vitamin A for poorer people- cows have a gene to make the protein antitrypsin in their milk which helps people with cystic fibrosis- faulty genes that cause disease can be put into animals and researched to find a cure

Disadvantages : We don’t know how an inserted gene will behave, other species might evolve as a result, the health of the animal may be affected

B3h: More of the Same Offspring produced as a result of asexual reproduction are called clones

Embryo transplanting means: fertilising a good egg e.g. from a healthy cow with sperm from a healthy bull, letting it divide, then inserting the dived cells into many cows so you get the same healthy offspring

Dolly the sheep was the first cloned mammal- the nucleus from normal sheep A’s body cell was put into an egg cell with no nucleus- this grew as if it was a zygote and was placed into the uterus of female sheep B- Dolly was born and was a clone of Sheep A

Cloned mammals are less healthy than ones produced by sexual reproduction, but we don’t know why

B3h: More of the Same We can use pigs organs to replace humans, but our body’s immune system attacks them

Researchers have been putting human genes into pig cells to stop this happening

Humans will be cloned eventually somewhere, identical twins are natural clones

Plants are cloned by humans taking cuttings or by plants forming tubers (potatoes) or runners (like the spider plant)

Advantages of cloned plants : identical plants for colour or flavour, some plants are hard to grow from seeds

Disadvantages of cloned plants : all die of the same disease, no new varieties

B3h: More of the Same Tissue cultures/micropropagation make large numbers of identical plants

Take a small piece of the plant (explant) spread them onto a growing medium they grow into a callus grow some calluses into other calluses new plants are formed when transplanted onto another medium put these plants in the soil

The tiny plants can become infected with fungi so must be disinfected

Plant cloning is easier than animal cloning as: many plant cells don’t differentiate, there are no stem cells in a human capable of producing all the different tissues in the body- salamanders are the exception and research is being done to find out why