Biology Unit 4 A-Level

A sequence of changes in a community

Over a period of time

Define Succession

Define Climax community

Final stage: Stable

Describe the structures in a chloroplast involved in the light-dependent reactions

Thylakoids made of membranes

Arranged as grana

Contain chlorophyll

Arranged as photosystems

Membranes contain ATPase

Electron carriers associated with thylakoid membranes

Advantages of growing crops in glasshouses with artificial light instead of open fields

Crops grown all year round

Plants photosynthesise 24 hours a day

Less physical damage due to weather and animals

Pest control easier

Control of temperature/water supply

Effects of carbon dioxide and methane on Earth's temperature

Greenhouse gases

Trap heat and infra red

Reflected from Earth's surface

Mean temperature of earth's surface increases

Suggest how other animals are affected by a fall in another population

Fewer prey eaten by the population

Therefore prey increase in number

Less competition for food from the population

Predator of the population might decrease, eat other prey or migrate

Define biotic factors

Factors involving organisms and living things

Define abiotic factors

Factors that are physical, chemical or non living

Species density quadrat experiment

Several readings

Use of random quadrat positions

Random number calculator

Known area of quadrat

Number of individuals in each quadrat counted

For mean density: total number of each species divided by total area sampled

Examples of abiotic factors

Light intensity, temperature, pH

Examples of biotic factors

Predators, food availability, disease, competition

Explain gene mutation

Change in DNA

A deletion/addition/duplication/substitution of bases

Enzyme used to amplify DNA

Polymerase

Process used to separate DNA fragments

Gel electrophoresis

DNA profiling - which is the suspect?

1. All of the bands in the sample must match

2. DNA profiling assumes every individual's DNA is unique

3. Apart from identical twins

4. DNA profiling analyses the introns/Short tandem repeats

5. Non-coding DNA is very variable

6. Large number of introns

7. Many combinations at each locus

Explain why DNA profiles are not absolutely conclusive

1. DNA profiling has several stages

2. Contamination can arise at any stage

3. Only a few sequences of DNA analysed

4. Possibility of two identical profiles from unrelated individuals

5. Identical twins may show same profile

Suggest how DNA profiling is useful when examining fossils

1. Comparison made between DNA from fossils and other organs

2. Find genetic relationships/how closely related

3. Used in taxonomy/classification

4. Understand evolutionary lines

Describe the genetic material in HIV

RNA

Linear nucleic acid

No plasmids

Describe the genetical material in TB

DNA

Circular nucleic acid

Plasmids

How does skin create a barrier against HIV

Keratin/protein in skin surface

Forms a hard, impenetrable layer

Explain the HIV infection process on T-lymphocytes

1. Glycoprotein (GP20) on virus binds with CD4 receptors

2. On surface membrane of lymphocytes

3. Viral RNA enters the lymphocyte

4. Viral RNA used to produce viral DNA

5. By action of reverse transcriptase

6. Formation of new viruses

7. Viruses bud out of the cell causing cell lysis to lymphocyte

8. T killer cell destroys infected t help cells

Effect of reduced number of t-lymphocytes

B cells not activated

Fewer antibodies

T killer cells increase

Explain how carbon dioxide and ammonia are formed during the first stage of decomposition

1. Microorganisms/bacteria/fungi in the faeces carry out respiration

2. Anaerobic or aerobic respiration

3. Converts organic compounds to carbon dioxide

4. Converts nitrogen compounds to ammonia

Effects of seasonality on rate of decomposition

1. Temperature effect

2. Water availability

3. Water logging reduces oxygen availability

4. Frozen water

5. More insects and decomposers in summer

6. Rate of growth of microorganisms

7. Rate of metabolism/enzyme reactions

Hygiene practices in hospitals

1. Strict hygiene practices

2. Hand washing regimes

3. Especially when dealing with open wounds

4. Wearing suitable clothing

5. Antiseptic solutions readily available (gels, pastes, alcohol rubs)

6. Screening of admissions

7. Monitor use of antibiotics

8. Fewer patients and visitors passing in and out

Prevent contamination of pillows in hospitals

1. Having a code of practice when dealing with hospital acquired infections

2. Clothing rules for workers

3. Improved laundry - increase frequency/higher washing temperature

4. Pillows treated with antibacterials/disposable pillows

5. Use special procedures e.g sealed plastic bags to carry pillows

6. Screening of patients

7. Hand washing regimes

Effects of a higher temperature on carbon fixation

Temperature changes movement of particles

Therefore effects the number of enzyme-substrate collisions

Why does food development depend on the rate of carbon fixation in plants

Carbon fixation produces GP

Product is converted into sugar/starch

Faster carbon fixation means faster sugar/starch production

Rate of growth depends on rate of carbon fixation

Increase GPP of crops

Suggest why countries may decide to drain marshy peatlands for the production of biofuels

1. Increased income

2. To export fuels

3. More jobs

4. Reduce imports of fossil fuels

5. Biofuels are renewable

6. Fossil fuels are finite

7. Reduce use of fossil fuels

8. No loss of farmland

Effects of clearing peatlands

Produces biofuels - combustion of biofuels releases carbon dioxide recently removed from the atmosphere - no net increase in atmosphere

CO2 is a greenhouse gas

Absorbs/traps infra red/heat - prevents it from escaping into space

Mean temperature of earth's surface increases

Carbon in peat was trapped from long time ago

Peatland clearing releases CO2

Net gain of CO2 in atmosphere

Removal of plants also reduces photosynthesis

CO2 released from clearance machinery

Symptoms of TB

Coughing, tubercules, blood sputum, body tissue wastage

Describe how TB organisms are taken up by macrophages

1. Bacterium recognised as non self

2. Labelling of bacteria by B cells

3. Phagocytosis

4. Macrophage engulfs bacterium

5. Formation of vacuole

What is a Cistron

Sequence of triplets on a section of DNA used to form a strand of pre-mRNA

Describe how free nucleotides are bonded together in the correct sequence in pre-mRNA

Sequence of bases on DNA determines sequence in pre-mRNA

Complementary base pairing

Formation of bonds by condensation reactions

Phosphodiester bonds

RNA polymerase

Function of codons at each end of a strand of mRNA

Start/stop codons

Start: needed to begin polypeptide synthesis

Stop: needed to end polypeptide sythesis

Suggest why a variety of structured could be formed from the polypeptides synthesised using the mRNA molecules from a single gene

Difference of exons/mRNA

Different primary structure

Secondary and tertiary structure of proteins depends on primary structure

Due to change in bonds

Hydrogen/disulphide bonds

Different 3D shape

Define gene pool

Total of all the alleles in a population

Define allele frequency

The number of times occurring for one allele within a gene pool

Suggest why Sardinians are placed as sub species instead of two separate species

If allowed to interbreed

Sub species could produce fertile offspring

How are new species formed (speciation)

1. Geographical isolation e.g. Volcanic eruption, the sea

2. Population cannot interbreed

3. Gene flow between populations restricted

4. Only a small number breeding

5. Limited variety of alleles

6. Mutation

7. Different selection pressures

8. Change in allele frequencies

9. Leads to physiological/behavioural/physical changes

How DNA profiling provides evidence of common ancestry

Bands produced at certain positions

Common bands contain similar DNA fragments

The more similar the patterns, the closer the relationship

Very few differences if still a sub-species

Why can MRSA bacterium produce several different clones of plasma cells that produce a variety of antibodies

1. Bacterium is made of many different polymers

2. Which can act as antigens

3. Individual b cells recognise specific antigens

4. Activation of b cells by t cells

5. Mitosis in b cells

6. Form genetically identical plasma cells

Advantage of using monoclonal antibodies

1. Specific antigen can be identified

2. Specific antibody binds to specific antigen

3. Specific treatment can be given

4. Avoids unnecessary use of drugs

5. More likely to be effective

Define GPP

Rate at which energy is incorporated into organic molecules in plants in photosynthesis

Define NPP

Rate at which energy is transferred into new plant biomass. Not all of the material is eaten (excretion,respiration,metabolism)

Suggest why DNA polymerase from a human source is not suitable for use in PCR

Human enzymes will not work at hight temperatures

Denaturation at temperatures in PCR

Suggest why identification of woody (xylem) plants cannot be done using PCR and DNA profiling

Xylem made of dead material/has no cytoplasm

No DNA present

Suggest how GALP may be used to synthesise cellulose

1. GALP is a 3C molecule

2. Formation of glucose from GALP

3. Cellulose consists of beta glucose

4. Joined by glycosidic bonds

5. 1,4 bonds

6. Condensation reactions

7. Cellulose is a long chain - polysaccharide

8. Unbranched molecule

How can scientists use temperature data to predict future climate change

1. Extrapolating data

2. Investigating correlations

3. Provide evidence of global warming

4. Using data along with other data sources

Suggest why patients are given antibiotics as part of their treatment against TB

TB is caused by bacteria

Antibiotics kill bacteria

Suggest why an increase in temperature may cause an increase in NPP

Rate of photosynthesis increases

Increases movement of enzymes and substrate

Increase rate in reaction because of more enzyme substrate interactions

Explain how HIV enters cells

1. HIV binds to CD4 receptors on cell surface

2. Glycoprotein on virus surface

3. Fusion of virus envelope with cell surface membrane

4. Phagocytosis in macrophages

Describe the sequences of events following infection of cells by HIV that may lead to death

1. Viral RNA

2. Production of DNA using viral RNA

3. Reverse transcriptase

4. Incorporation of viral DNA into host's DNA

5. Integrase

6. Production of viruses

7. Infection of further T helper cells

8. Destruction of T helper cells by cell lysis

9. Lowering immunity to other diseases

10. T helper cells cannot produce cytokines to activate B killer cells

11. Death caused by opportunistic diseases e.g TB

Suggest why the bacteria are not visible in the photograph

1. Too small

2. Not stained

3. Already removed by phagocytosis

4. Bacteria not present in sample shown

Characteristic features of antibodies

1. Glycoprotein

2. Disulphide bridges between peptides

3. Antigen-binding site

4. A similar region

5. Present on B cells

Describe how artificial immunity can result in immunity against HIV

1. Vaccination

2. Contains glycoproteins/synthetic molecule/antigen

3. Stimulates the specific immune response

4. T helper cells activate B cells

5. B memory cells made

6. Antibodies are produced faster on reinfection

Suggest why data about HIV infections are often estimates

1. HIV virus does not always produce symptoms

2. Latency (virus is dormant)

3. Test needed to detect HIV

4. Only people who suspect they may have it get tested

5. Some people do not want to be tested/cant test everyone

6. Symptoms common to other diseases

Describe how a small sample of DNA can be amplified

1. Polymerase chain reaction

2. Polymerase enzyme added

3. Need for primers and nucleotides

4. 95 degrees, 55 degrees, 72 degrees

5. Cycle needs to be repeated several times to make several copies of DNA

Suggest how scientists had their results accepted by others

1. Work appearing in a scientific journal or presented at a conference

2. Validity or reliability considered by other scientists

3. Peer reviewed

Suggest how geographical isolation results in two separate species

1. Different environmental conditions in each region

2. Different selection pressures

3. Restricted gene flow/separate gene pools

4. Reproductive isolation

Suggest how gene mutation results in two separate species

1. Different gene pools

2. Leads to new phenotypes

3. New alleles can be advantageous

4. Advantageous alleles passed on to offspring

Suggest why inbreeding does not take place between two populations

1. Different species reproductively isolated

2. Different breeding times

3. Different breeding behaviours (different sized genitalia)

4. Breeding between different species results in infertile offspring

Explain why the light independent stage cannot take place without the light dependent stage

1. Products of light dependent stage are needed for light independent stage

2. Products of light dependent stage are reduced NADP and ATP

3. ATP used as source of energy

4. Reduced NADP used for reduction of carbon dioxide

Suggest why it is important to conserve rare plants

1. Conservation of genetic variation

2. Prevent extinction

3. Aesthetics

4. Medicinal uses

5. Other animals depend on these plants (source of food/habitat)

Suggest why protecting reserves is likely to be more successful than captive breeding programmes

1. Less stress for animals

2. Animals more likely to breed in natural environment

3. Animals may require large areas

4. Problem releasing into wild i.e habituation

5. Disease is less likely

6. Allowing natural communities to exist

7. Allowing natural behaviour

8. Large numbers needed for wide gene pool

9. Natural diet available

Suggest how time of death can be determined several days after being killed

1. Succession

2. Forensic entomology

3. Insects e.g flies, beetles

4. Life cycle stages of insects used

5. Decomposition

6. Different stages of decomposition and decay

7. Bloating, discolouration, gases

8. Rate of succession influenced by external factors

9. Insect and decomposition info used to determine time of death

Role of interferons

1. Involved in viral infections

2. produced by infected cells

3. Inhibits replication of viruses

Role of lysozymes

1. An enzyme

2. Present in secretions

3. Kills bacteria

4. Specific active site

5. Acts on cell wall of bacteria

Why may inflammation be the result of a bug bite

1. Histamine released as a result of damaged cells

2. Released by mast cells

3. Arterioles dilate, capillaries more permeable, vasodilation

4. Oedema, swelling, redness, heat

Suggest why applying an antihistamine cream may be better than taking tablets

1. Only a local reaction produced

2. Cream applied to actual site of production of histamine

3. Treatment more rapid

4. Higher concentration at site

5. Tablets may lower immune response/lead to side effects

Suggest how a microscope slide could be prepared to observe cell division in T helper cells

1. Making slide of T cells from blood

2. Stain with acetic orcein

3. Heating stain, using acid

4. Looking for mitotic features

Role of T helper cells in the immune response

1. Release cytokines

2. Activating B cells

3. Antibody production by plasma cells

4. Involvement in activating T killer cells

5. Which destroy infected cells

Role of the Golgi apparatus in T helper cells

1. Protein modified

2. E.g cytokines

3. CD4 receptors

4. Exocytosis

Factors that can affect time of death

1. Clothing

2. High BMI

3. Body curled up/buried/in water

4. Fever

Forensic entomology experiment

1. Range of temperatures - at least 5

2. In a water bath/incubator

3. Timing starts when new stage of life cycle appears

4. Stops when next stage appears

5. Several organisms used at each temperature

6. Providing food for organism

7. Controlled variables i.e mass of food, species, humidity

8. Total length of life cycle can be measured

Explain the importance of sequences of bases in a gene

1. Triplet coding system

2. Sequence of bases determines primary structure

3. Importance of primary structure in 3D structure

4. Start sequences

5. Stop codons

Explain how one gene can give rise to different channel protein in hair cells

1. Transcription

2. Splicing of pre-mRNA

3. Spliceosomes

4. Removal of introns

5. Exons arranged in different combinations

6. mRNA is different

7. Translation

8. Different primary structure

9. Results in different bonds

Suggest reasons why 95% of light hitting the surface of a leaf is not used by the cholorplasts

1. Reflection

2. Incorrect wavelength

3. Not hitting chloroplast - it is transmitted

4. Light being in excess i.e at maximum photosynthesis

Explain how energy from light is made available in ATP molecules

1. In thylakoid membranes

2. In grana

3. Light energy raises energy level of electrons - excited

4. Electrons released from chlorophyll

5. Electron carrier

6. Series of redox reactions

7. Energy level of electron falls

8. Synthesise ATP from ADP + Pi

9. Photophosphorylation

10. ATPase

11. Chemiosmosis

12. Electrons from photolysis used to replace those lost

Explain why phagocytosis will only happen in response to some types of bacteria and not others

1. Protein nature of antibodies

2. Antigens are specific to each bacteria

3. Antibodies need to be specific to the antigen

4. So that binding can take place

5. Some bacteria have different antigens

6. This is primary infection

7. Mucus/slime capsule of bacteria

8. Some bacteria inside body cells

9. Antibodies already present

Describe how bactericidal antibiotics work

1. Weakens the cell wall so it cannot form properly

2. Cell wall bursts easily

3. During division

Explain why doctors have been advised to limit the prescription of antibiotics

1. Antibiotics acting as selection pressure

2. Some bacteria resistant

3. Resistant bacteria survive and reproduce to pass on gene

4. Antibiotic no longer effective

5. Some infections cannot be treated with antibiotics

Effects of different antibiotics experiment

1. Bacteria distributed evenly using lawn spreading

2. Method used to apply different antibiotics e.g multidisks

3. Control antibiotic concentration

4. Aseptic technique

5. Incubation at suitable temperature

6. Measure zone of inhibition

7. Replication with same bacterium

8. Repeat with different bacteria

Suggest why the seedlings were germinated at 18 degrees before being placed in temperature controlled rooms when experimenting effects of temperature on mean dry mass

1. Controlling a variable

2. Optimum temperature for germination

3. Making sure seeds germinate

4. For validity of the experiment

Suggest why temperatures below 0 and above 40 degrees would be unsuitable for most organisms

1. Below 0 degrees enzymes inactive

2. Because lower kinetic energy

3. Above 40 degrees enzymes denature

4. Fewer enzyme-substrate complexes possible

5. Change in active site/change in bonding

Suggest why scientists do not agree that a reduction in fossil fuels will prevent further global warming

1. CO2 produced by using fossil fuels

2. No direct evidence that increased CO2 leads to global warming

3. CO2 released from other processes

4. Removal of carbon sinks also leads to increase in CO2

5. Methane also released from cows

6. Natural cycles may be involved in global warming e.g volcanoes

7. Evidence from the past being used

8. Past evidence not an indicator of future events

9. Scientists may be biased

Suggest why the type of plant community growing on a bing changes over time

1. First pioneer species - mosses and lichens

2. Able to grow with no soil

3. Breaks up rock fragments to form shallow soil

4. Plants with small roots able to grow in soil

5. Change in soil structure enables trees to grow

6. Soil able to hold water and minerals

7. As plant decay organic matter released

8. Competition effects

Explain why a climax community is stable

1. Includes both animals and plants for high biodiversity

2. Interaction between species

3. Balanced equilibrium of species

4. Dominant species

5. Stable if no change in environment

Differences between fibrous and globular proteins

1. Fibrous - long straight chains

2. Globular - compact, spherical

3. Globular folded fibrous not

4. Globular soluble fibrous not

Ways in which skin flora can help protect a person from infection by pathogenic bacteria

1. Competition for nutrients

2. Competition for space

3. Secretion of chemicals e.g lysozyme

4. Stimulation of skin immune system

Explain how oxygen is produced during the light dependent stage of photosynthesis

1. Energy from light

2. Photolysis

3. Of water

Suggest why treatment for HIV will require continual development of a mixture of many new drugs

1. HIV has many antigens

2. Some strains resistant to particular drug

3. These would survive if only one drug used

4. Mixture of drugs has more chance of getting rid of all strains

5. Drug used together because of mutation

6. Rapid rate of mutation

7. Rapid rate of multiplication of virus

Suggest how core body temperature and ambient temperature can be used to measure time of death

1. Core temperature related to time of death

2. Drop in core temp depends on ambient temperature

3. Cooling curve

4. Temperature affects rigor mortis

5 evidence can be combined

Explain what is meant by reproductively isolated populations

1. No interbreeding

2. Because of geographical barrier

3. Different behavior

4. Incompatible genitalia

5. Each population have restricted gene flow

Describe how the vaccine gives active immunity against PWMS

1. Using virus as vaccine

2. Which is modified so harmless

3. Vaccine contains antigen

4. Activation of specific B cells

5. Production of B memory cells

6. Body now able to produce specific antibody faster on exposure

Describe how GALP is formed in the light dependent reactions

1. GALP formed in calvin cycle

2. Carbon fixation i.e CO2 reacts with RuBP

3. Forms GP

4. RUBISCO as an enzyme in carbon fixation

5. Formation of GALP

6. Using ATP and NADPH

Light intensity on seedlings experiment

1. Planting seeds and measuring height

2. For a certain period of time e.g 2 weeks

3. Range of light intensities i.e 5

4. Repeat at least 3 times

5. Calculate mean

6. Control variable e.g pH, temperature

How can global warming affect tree ring growth

1. Increase temp increases tree ring growth

2. Enzymes work faster with higher temp

3. Photosynthesis faster

4. More biomass laid down in tree trunks

5. Above certain temperature rate of enzyme activity decreases

6. Enzymes denature at high temp

Describe how microorganisms decompose organic matter

1. Bacteria and fungi

2. Enzymes involved in decomposition

3. Enzymes secreted onto organic matter

4. E.g protease

5. On protein, lipid, polysaccharide

6. Decomposition produces e.g amino acids

7. Bonds broken e.g peptide bond

8. Dissolved

9. Some soluble molecules taken up and used by microorganisms

Why pH affects growth of bacteria

1. pH affects enzymes

2. Shape of active site altered

3. E.g respiration affected

4. pH may affect cell wall structure