B2 Topic 2

B2.1 – Plant and Animal Cells

7 Organelles Function

Cell Membrane Controls movement into and out of the cell.

Nucleus Contains DNA. Controls the cell

Cytoplasm Where chemical reactions take place.

Mitochondria Where respiration occurs.

Cell Wall Made of CELLULOSE. Supports the cell.

Vacuole Contains CELL SAP. Helps support the plant by keeping the cell rigid

Chloroplast Contains CHLOROPHYLL. Absorbs LIGHT. Where photosynthesis takes place

Plant and animal cells can be studies in greater detail using a light microscope. Light passes through a thin slice of the specimen. Lenses magnify the specimen many times.

B2.2 – Inside Bacteria

4 Organelles Function

Chromosomal DNA A giant loop of DNA containing most of the genetic material.

Plasmid DNA Small loops of DNA that carry extra information.

Flagella Long whip like structures that aid movement.

Cell Wall Provides support but is more flexible than a plant. Not made of cellulose.

2 types of DNA

Microscopes have improved in last 350 years. Light microscopes can magnify 1500x.Electron microscopes can magnify 2000000x. Electron microscopes produce very clear images.Electron microscopes show more detail of the specimen.

B2.3 - DNAKey DefinitionA gene is a section of DNA that codes for a specific protein.

DNA is made up of two strands coiled to form a double helix. The two strands are linked by complementary bases held together by weak hydrogen bonds.

Adenine (A) pairs with Thymine (T)Cytosine (C) pairs with Guanine (G)

B2.4 – Extracting DNA1. Chop onion or peas into chunks. 2. Grind in a pestle and mortar.3. Mix together with washing up liquid, salt and water and stir.4. Incubate the mixture at 60 degrees Centigrade for 15 minutes

in a water bath.5. Filter the mixture through filter paper into a boiling tube. 6. Take ice cold alcohol and pour it slowly down the side of the

boiling tube. The alcohol will form a transparent layer on top of the liquid, as the alcohol is less dense.

7. You will see the DNA between the two liquid layers.

B2.5 – DNA DiscoveryLondon - Maurice Wilkins & Rosalind Franklin using X-rays to study DNA structure. From the patterns made they could work out how the atoms were arranged.

Cambridge – Watson & Crick were building a model of DNA using data from other scientists. They were given a copy of Franklins photographs which enabled them to crack the code. Franklin didn’t know they had the photo.

Watson and Crick published their paper with the structure of DNA but didn’t acknowledge the photograph they used

Watson and Crick were awarded the Nobel Prize with Maurice Wilkins but Rosalind Franklin had already died so did not get the prize.

B2.5 – DNA DiscoveryThe Human Genome Project – International Project.

3 billion bases that make up the human genome were sequenced. It took 13 years and scientists collaborated using IT to store and share data.

All humans have 99.9% of their DNA in common.

5 Implications of the HGP1. Improved genetic testing for

disorders. 2. New ways of finding new genes

that may increase risk of certain diseases.

3. New treatments and cures for diseases.

4. New ways of looking at changes in the genome over time.

5. Personalised medicines that work with a particular genotype.

B2.6 – Genetic Engineering

Know this process!

Definition - The process of removing a gene from one organism and inserting it into the DNA of another.

B2.6 – Genetic EngineeringExample Advantages Disadvantages

Beta carotene in golden rice to reduce vitamin A deficiency in humans

1. Beta carotene used to make vitamin A

2. Vitamin A will reduce death and blindness.

1. Could cross breed with wild rice and contaminate wild rice DNA

2. Levels of beta carotene in Golden Rice might not be high enough to make a difference

3. Can be expensive to buy4. Produces sterile seeds so farmers

have to buy them every yearThe production of human insulin by GM bacteria

1. Can be used by vegans2. Supply not affected by animal

diseases3. Supply not affected by demand for

meat4. Can be made in vast quantities5. Cheaper

1. Bacteria produce insulin slightly differently so may not work for some people

The production of herbicide resistant crops

1. Reduces amount of crop spraying 1. Herbicide resistant weeds can develop

2. Cross pollination with wild plants3. Potential loss of biodiversity

B2.7 – Mitosis and Meiosis

Mitosis• The production of two

daughter cells with identical sets of chromosomes in the nucleus as the parent cell.

• Results in the formation of two genetically identical diploid cells.

• Occurs during growth and repair and asexual reproduction

Meiosis• The production of four

daughter cells, each with half the number of chromosomes as the parent cell.

• Results in the formation of genetically different haploid gametes.

• Occurs when making gametes only.

DefinitionsHaploid – Having one set of chromosomes. Diploid – Having two sets of chromosomes.

Gamete – the sex cells (sperm and egg)

At fertilisation, haploid gametes join to form a diploid zygote.

B2.8 - Clones

How to produce a clone1. Remove a diploid nucleus from

a body cell2. Enucleate an egg cell3. Insert diploid nucleus into

enucleated egg cell.4. Stimulate the diploid nucleus

to divide by mitosis.5. Implant into surrogate mother.

Cloning – An example of asexual reproduction.

Enucleate – Remove the nucleus

B2.8 - ClonesAdvantages of Cloning

Disadvantages of Cloning

Risks of Cloning

1. Can make a genetically identical copy of an animal with desirable characteristics.

2. Can be used to make copies of GM animals to guarantee all offspring have the trait.

1. Cloned animals often die young.

2. Cloned animals often age more quickly.

3. Complicated process.

1. Very few embryos develop properly resulting in deformities.

B2.9 – Stem Cells

Advantages of Stem Cell Research

Disadvantages of Stem Cell Research

Risks of Stem Cell Research

1. Embryonic stem cells can develop into almost every type of human cell.

2. Bone marrow stem cells can be used to treat lukaemia.

3. Adult stem cells may be used in future instead of embryonic stem cells.

1. Embryonic stem cells can come from leftover embryos from fertility treatments.

2. Risk of rejection if not from a patients own stem cells.

3. Could lead to tumours forming.

1. Technology could be used illegally.

2. Risk of the unknown – long term effects may not be shown for years.

Key definitionsStem Cell - An unspecialised cell that can divide to produce more stem cells or different types of specialised cell. Differentiate – Become specialised. Embryonic Stem Cell – Can differentiate into almost any cell type.Adult Stem Cell – Can differentiate into only a few cell types. Specialised Cell – a cell with a particular function e.g. neurone, red blood cell.

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B2.10 Protein Manufacture

Transcription1. DNA double helix unzips.2. The complementary mRNA strand is made in the nucleus and passes

out through a pore.

Translation3. mRNA attaches to the ribosome.4. A triplet of bases on the mRNA (codon) code for a specific amino acid. 5. tRNA transfers amino acids to the ribosome.6. Amino acids link together to form polypeptides.

RNA is single stranded but DNA is double stranded. RNA contains Uracil (U) instead of thymine (T)

Each amino acid is coded for by 3

specific bases. DNA is a triplet code.

B2.11 - Mutations

1. Each protein has its own specific number and sequence of amino acids.

2. This is coded for by the DNA. 3. Therefore, each protein is a different shape and has a

different function e.g. an enzyme.4. Mutations change the sequence of the bases, and therefore

the shape of the protein. 5. Most mutations are harmful. 6. Radiation and some chemicals in cigarette smoke are

mutagens and cause mutations.

Mutation – A change in the sequence of bases in the genetic code.

B2.12 - Enzymes

These are examples of enzyme catalysed reactions:1. DNA Replication – One enzyme unzips the two strands of

DNA, the other joins the new bases together to make the new double stranded molecule.

2. Protein Synthesis – RNA Polymerase makes the mRNA strand from the DNA template.

3. Digestion – Many enzymes break larger molecules down into smaller ones in digestion. This happens outside of the body. Stain digesting enzymes in washing powders break down stain in clothes. Microorganisms excrete enzymes onto food to break them down outside the body and then absorb the products.

Enzymes are biological catalysts. They speed up reactions.

B2.13 – Enzymes and Temperature

Factors that affect enzyme activity:1. Temperature2. pH3. Substrate Concentration.

Enzymes are SPECIFIC to their substrate. They only catalyse specific reactions in specific conditions. They have a specific

shaped active site.

Enzyme activity can be measured by measuring the speed at which a product is made e.g. a gas, or the speed at which a

substrate is used up e.g. stain digestion.

B2.14 – Enzyme ActionAs temperature

increases, so does enzyme activity, up to 40oC. After 40oC the

active site is denatured and the reaction stops.

As substrate concentration increases, so does enzyme

activity, up to a point where the number of active sites becomes limiting. The only way to speed up the reaction after this is to increase the number of active

sites.

Enzymes will only work at a specific pH. Either side of this optimum pH, the enzyme will denature and not

work.

Enzymes can never be killed. They can only be denatured, which is where the

shape of the active site changes.

B2.14 – Enzyme Action

Enzymes work like a lock and key Lock and Key Enzyme and SubstrateOne key will only fit one lock. One substrate will only fit one enzyme. The key fits the lock. The substrate fits the active siteThe key unlocks the lock. The substrate is changed in the enzymeWrong key won’t fit the lock. Wrong substrate won’t fit the active site.

B2.15 Aerobic Respiration.

• All organisms are made of cells • Energy released by respiration • Cells that move more need more energy.• Exercise = more energy needed.

Key Terms:Respiration - the release of energy from food molecules that act as fuel for the cell.Diffusion - when substances move from an area of high concentration to an area of low concentration.

Glucose + Oxygen = Carbon Dioxide + Water

Aerobic respiration = uses oxygen to release energy from glucose.

How does it get delivered?• Glucose and oxygen diffuse from capillaries to respiring cells• Carbon dioxide diffuses from respiring cells to capillaries• Capillaries - smallest vessel that carries blood between cells/ one cell thick• Substances move by diffusion down a concentration gradient = the diffusion

pathway.

• Respiring cells = oxygen and glucose levels fall as they are used up in aerobic respiration/ Carbon dioxide levels increase.

• Gas exchange = the transfer of gases.

B2.16 investigating The effects of exercise.

• Exercise = increase heart rate and has to pump blood faster to the muscles.

• Causes breathing rate to increase and get deeper.

Why?• Cells need more oxygen and glucose as they need

more energy. • Cells produce more carbon dioxide as a result

which needs to be removed.

B2.17 Anaerobic respiration

• Anaerobic respiration = respiration without oxygen• Glucose is broken down to supply energy to the muscles• Releases less energy then aerobic and produces Lactic Acid• Amount of blood pumped around the body depends on the stroke volume and the

heart rate.• Exercise = increase in heart rate and stroke volume.• Lactic Acid needs to be broken down = oxygen used to break it down into carbon

dioxide and water. • The requirement of this oxygen to break down the lactic acid is called excess post-

exercise oxygen consumption (EPOC)

Glucose lactic acid

Cardiac output = stroke volume x heart rate.

B2.18 Photosynthesis.

• Photosynthesis = plants make their own food• Uses light energy to produce glucosefrom carbon dioxide and water• Glucose stored as starch• Starch = lots of glucose molecules joined together.• Digestion breaks down starch = glucose• Chlorophyll = green found in chloroplasts absorbs light for

photosynthesis.• Variegated leaves = the green parts of a leaf contain the chlorophyll.

Carbon dioxide + water glucose + oxygenLight and chlorophyll

2.20 Factors that effect the rate of photosynthesis.

3 factors that effect photosynthesis.

• Carbon dioxide• Light• Temperature

• All 3 are needed at optimum amount for photosynthesis to be at its best.• The limiting factor is the one that is in short supply…..you may have lots of CO2 the right

temperature but little light this means photosynthesis will be slow.

Limiting factor = something can affect the rate of photosynthesis.

Adaptations of a leaf.Upper epidermis = tightly packed cells = lots of chloroplasts = lots of photosynthesis.

Air spaces = provide large surface for cells to exchange with gases in the air.

Lower epidermis = contain stomata.

Stomata = open and close to allow gases into the leaf. Located underside of the leaf.

Open in response to light.

Allow Carbon dioxide in and lets out oxygen and water vapour.

3 Adaptations

Has stomata for gas exchange (carbon dioxide, oxygen, water vapour)

Contains chlorophyll in chloroplasts to absorb light.

Large surface area to absorb most amount of light.

Root Hair Cell

• Job of root = anchor plant and take up nutrients.

• Root hair found on surface of root.

• Role – to absorb water and dissolved minerals.

• Adaptation = large surface area.

B2.21 Water Transport

• Roots absorb nitrates and mineral ions dissolved in water by Active transport. This needs energy from respiration

• Water transported by xylem• Nutrients transported by phloem

Key Definitions• The loss of water from the leaves drives

transpiration.• Transpiration – the movement of water

through a plant and the loss of water throught he leaves.

• Osmosis = movement of water from an area of low concentration to an area of high concentration through a partially permeable membrane.

B2.22 Investigating Osmosis

OsmosisWater can move across cell membranes because of osmosis. For osmosis to happen you need:two solutions with different concentrations anda partially permeable membrane to separate them

B2.23 Organisms and their environment

Key Terms• Environment = an organisms

surroundings including the soil, air, water and other organism in the area.

• Biodiversity = the different plants and animals in an area.

• Ecosystem = an area in which all the living organisms and all the non living organism form a relationship in order to survive.

• Habitat = where the plants and animals are found/living.

• Population = the number of animals in a given area.

• Sampling = looking at small proportion of the plants and animals.

Sampling techniques = • 1) Pooter = used to catch animals.• 2) Sweep net = can catch flying

animals.• 3) Pond net = to catch aquatic

animals. • 4) pit fall traps = buried in the

ground…the organisms fall in. • 5) quadrats = used to sample the

population size of plants = random sampling or systematic sampling. = placing the quadrat at regular intervals along a line.

B2

Topic 3 Common Systems

B2.25 Fossils and evolution

Keywords• Fossil record – The collection of fossils identified from different periods of time that can be

interpreted to form a hypothesis about the evolution of life on Earth.• Fossil – The preserved traces or remain of an organism which lived a very long time ago• Pentadactyl – five fingered organism

Facts:• The moon is 30 ‘earths’ away• The sun is 11,000 ‘earths’ away

Fossils• Fossils from different periods of time show organisms have changed gradually = evolution.• Fossil record has gaps

– Soft tissues decay not forming fossils– Hard parts of organisms could have been destroyed– Many fossils are buried too deep to be found

• Scientists using incomplete data sometimes make mistakes• More fossils = more accurate conclusions

Evidence for Evolution• Internal bones of all vertebrate’s limbs are similar• Fossils of limbless vertebrates have the same five fingered structure• All vertebtates evolved from one common ancestor• Evolution of the limbs is due to adaptation to how the organisms lived and moved,

B2.26 GrowthKeywords• Percentile – The value of a variable below which a certain percentage of observations fall.• Stem Cell – An unspecialised cell that can divide to produce more stem cells or different kinds of specialised cells• Differentiate – Specialise, develop into different kinds of cell, as in cells that become nerve, muscle or bone cells• Elongation – getting longer

Facts• Growth is when an organisms

increases in size, length and mass

• To monitor growth of babies we check– Head circumference– Weight– Height

• Each child is compared to a chart to determine which percentile of the population they are in.

• Growth involves 2 things

– Increase in the number of cells

– Increase in the size of cells

Growth in Plants• Grow all through their lives• Cells divide in the Meristem – behind the tip of the root and shoot• Cells also elongate• Older meristem cells differentiate to become specialised for example:

– Palisade leaf cell– Root hair cell

Growth in Animals• Cell division • Animals stop growing when they become adults• Stem cells are undifferentiated• Stem cells can specialise into all other cells• Adults have very few stem cells (only in blood and

skeletal tissues)• Most animals cannot regrow limbs or body parts.

Components

• Plasma– Fluid part of blood– Transports carbon dioxide, hormones and waste– Pale yellow

• Red blood cells– No nucleus = more room for haemoglobin– Made in the bone marrow. – Contain red pigment haemoglobin which carries oxygenOxygen + Haemoglobin Oxyhaemoglobin– Oxygen is carried in the blood to the tissues for aerobic respiration– Biconcave disc = large surface area to volume ratio for faster diffusion of oxygen

• White blood cells– An important part of the immune system– Some produce antibodies (proteins that bind to microbes and destroy them)– Others surround and destroy foreign cells– All have a nucleus– Made in the bone marrow– All have a nucleus

• Platelets– Tiny fragments of cells (no nuclei)– Clump together to form clots– Protect the body by stopping bleeding and forming a scab to stop microbes entering.

B2.27 Blood

B2.28 The heart

• Deoxygenated blood (low oxygen levels)

• Pumped to the lungs (by right ventricle) to collect oxygen

• Oxygenated blood returns to heart (Left side)

• Pumped to the body cells and tissues (by left ventricle)

• Left and right side work together at the same time

• Valves prevent backflow of blood

• Tendons stop valves turning inside outSeptum

Thicker wall as it pumps blood all around the body

B2.29 The circulatory system

3 types of blood vessel:Arteries• Carry blood away from the heart• Have thick muscular walls• Have small internal lumen• Blood under high pressureVeins• Carry blood to the heart • Thin walls• Larger internal lumen• Blood under low pressure• Valves to prevent blood flowing

backwardsCapillaries• Wall is one cell thick• Very low blood pressure• Allows diffusion between blood

and tissues

B2.30 The digestive system

churns

Peristalsis• Muscles contract

in waves to move food along the alimentary canal ( a muscular tube running from your mouth to your anus)

B2.31 Breaking down food

KeywordsEnzyme – a protein molecule made by living cells that speeds up the rate of a reactionEmulsion – a mixture in which particles of one liquid are suspended in another liquid.

Digesting proteins Digesting Carbohydrates

Digesting Fats

Enzyme involved

Proteases (e.g. pepsin)

Carbohydrases (e.g. amylase)

Lipases

Broken down into…

Amino acids Simple sugars (glucose)

Glycerol and Fatty acids

Where it occurs Stomach first then small intestine

Mouth and small intestine

Small Intestine

Additional features

Pepsin has an optimum pH of 2 (perfect for stomach acid)

Amylase is denatured by stomach acid

• Bile from the gall bladder breaks down large fat globules into droplets with a larger surface area to help lipase.

• We say bile emulsifies the fat.• Bile also neutralises the

stomach acid.

B2.32 Villi

Inside the Small Intestine1. Digested food passes into blood by diffusion2. Bigger surface areas = more diffusion3. Finger-like folds called Villi increase surface area of small intestine

Features of a Villus to speed up diffusion4. Good network of capillaries moving absorbed nutrients5. Low concentration of food6. Steep concentration gradient maintained7. Wall is a single cell layer (shorter distance to diffuse)

KeywordsVilli – finger like projections in the small intestine.Diffusion – movement of particles from an area of high concentration to an area of low concentration down a concentration gradient.

B2.34 Probiotics and Prebiotics – Functional foods

Prebiotics• Substances the body cannot digest• They act as food for the beneficial bacteria• Oligosaccharides are a common form of prebiotic (contained in tomatoes, onions and asparagus)• Also found in specially made dairy foods and sold as capsules• Increasing evidence supports their positive effect on health

Plant Stanol Esters• Oily substances in plants• Stop the small intestine absorbing cholesterol• Lowers blood cholesterol• Use in many foods like yogurt and spreads.

Probiotics• Live bacteria – friendly or beneficial• Bifidobacteria or Lactobacillus• They produce lactic acid in your gut and companies claim they improve health• NOT ENOUGH EVIDENCE to support the claims they are effective