Scottish Higher Higher Biology Syllabus

What is a single-gene (point) mutation, and name three types.

A point mutation is a change in a single nucleotide base. Types: substitution (one base replaced by another), insertion (an extra base added), and deletion (a base removed).

Why do insertion and deletion mutations usually have a greater effect than substitution?

Insertions and deletions cause a frame-shift, altering every codon (and therefore every amino acid) after the mutation point. A substitution affects only one codon, so its effect is usually limited to a single amino acid (or none).

Distinguish between missense, nonsense and splice-site substitution mutations.

Missense: one amino acid is changed for another. Nonsense: a codon becomes a premature stop codon, producing a shorter protein. Splice-site: the mutation affects intron/exon boundaries, so introns may be retained or exons lost in the mature mRNA.

Name and describe four types of chromosome structure mutation.

Deletion (a section of chromosome removed), duplication (a section repeated), translocation (a section moved to another chromosome), and inversion (a section reversed end to end).

How can gene duplication contribute to evolution?

Duplication produces an extra copy of a gene; the spare copy can mutate and evolve a new function while the original retains its role, providing raw material for evolutionary change without losing the original function.

Define natural selection and explain its role in evolution.

Natural selection is the non-random increase in frequency of advantageous alleles (or decrease of harmful alleles) in a population. Individuals with favourable variations survive and reproduce more, passing on those alleles, leading to evolution over generations.

Compare stabilising, directional and disruptive selection.

Stabilising selection favours intermediate phenotypes (reduces variation). Directional selection favours one extreme (shifts the mean). Disruptive selection favours both extremes against the intermediate (can lead to two distinct forms).

What is speciation and what is the role of isolation barriers?

Speciation is the formation of new biological species from existing ones when gene flow is prevented. An isolation barrier (geographical, ecological or behavioural) separates sub-populations so that mutation, natural selection and genetic drift act independently until they can no longer interbreed.

Distinguish allopatric from sympatric speciation.

Allopatric speciation occurs when a population is split by a geographical barrier (e.g. mountains, water). Sympatric speciation occurs without geographical separation, through behavioural or ecological isolation barriers within the same area.

What is genomic sequencing and what can be determined from it?

Genomic sequencing is determining the order of nucleotide bases in an organism's entire genome. It allows comparison of genomes within and between species and can be used to identify genes and study evolutionary relationships.

Define phylogenetics and explain what a phylogenetic tree shows.

Phylogenetics is the study of evolutionary relationships among organisms using sequence data. A phylogenetic tree is a diagram showing the lineages and relatedness of species, with branch points representing common ancestors.

What is a molecular clock and how is it used?

A molecular clock uses the rate at which sequence differences (mutations) accumulate over time to estimate how long ago species diverged from a common ancestor. The more sequence differences, the longer ago the divergence.

State the three domains into which sequence data have grouped all living organisms.

Bacteria, Archaea, and Eukaryotes (Eukarya).

What is personalised (pharmacogenomics) medicine, based on genomic sequencing?

It is the use of an individual's genome sequence to predict the likelihood of developing certain diseases and to select the most effective drugs and dosages for that person, improving treatment and reducing adverse effects.

Define an anabolic and a catabolic reaction, and state which releases energy.

Anabolic reactions build up large molecules from smaller ones and require energy. Catabolic reactions break down large molecules into smaller ones and release energy.

What is the difference between reversible and irreversible steps in a metabolic pathway, and what are alternative routes?

Reversible steps can proceed in either direction depending on conditions; irreversible steps proceed in one direction only. Alternative routes bypass steps, allowing the pathway to be controlled and to respond to cell needs.

Explain how enzymes control the direction and rate of metabolic pathways.

Each step is catalysed by a specific enzyme. The presence and quantity of enzymes determine which reactions occur and how fast. Enzymes lower activation energy, and most pathways are controlled by the availability and activity of their enzymes.

Describe the induced-fit model of enzyme action.

The active site is not an exact fit for the substrate initially; as the substrate binds, the active site changes shape slightly to fit more closely around it. This raises the affinity for the substrate and lowers the activation energy, then returns to its original shape after product release.

Distinguish competitive from non-competitive inhibition of enzymes.

Competitive inhibitors bind to the active site, competing with the substrate; their effect can be reversed by increasing substrate concentration. Non-competitive inhibitors bind elsewhere, changing the active site shape; increasing substrate concentration does not reverse this.

What is end-product (feedback) inhibition?

When the end product of a metabolic pathway accumulates, it inhibits an enzyme earlier in the pathway (often the first), switching off production until levels fall. This prevents wasteful overproduction.

State the role of ATP and the reaction by which it stores and releases energy.

ATP transfers energy in cells. Energy is stored when a phosphate is added to ADP and released when ATP is broken down: $$\ce{ADP + Pi <=> ATP}$$ The reverse (hydrolysis of ATP to ADP + Pi) releases energy for cellular work.

State the role and location of glycolysis, including its net ATP and end product.

Glycolysis occurs in the cytoplasm and breaks glucose (a 6-carbon sugar) into two molecules of pyruvate (3-carbon). It uses 2 ATP in the energy investment phase and produces 4 ATP, giving a net gain of 2 ATP, and releases hydrogen ions and electrons.

Where does the citric acid cycle occur and what are its products?

The citric acid cycle occurs in the matrix of the mitochondria. Acetyl group (from pyruvate, joined to coenzyme A) combines with oxaloacetate to form citrate. It releases $\ce{CO2}$, generates ATP, and releases hydrogen ions and electrons picked up by NAD.

Describe the electron transport chain and the role of oxygen as the final electron acceptor.

On the inner mitochondrial membrane, electrons released from hydrogen are passed along carrier proteins, releasing energy that pumps $\ce{H+}$ across the membrane. The flow of $\ce{H+}$ back through ATP synthase generates ATP. Oxygen is the final electron acceptor, combining with hydrogen to form water: $$\ce{4H+ + 4e- + O2 -> 2H2O}$$

What is the role of NAD (a dehydrogenase coenzyme) in respiration?

NAD accepts hydrogen ions and electrons (becoming NADH) released during glycolysis and the citric acid cycle, then delivers them to the electron transport chain where the energy is used to generate ATP.

Explain how fats and proteins can be used as alternative respiratory substrates.

Proteins are broken into amino acids (deaminated) and fats into glycerol and fatty acids; these are converted into intermediates of glycolysis or the citric acid cycle and metabolised. Fats yield more ATP per gram because they have more hydrogen for the electron transport chain.

Define metabolic rate and state three ways it can be measured.

Metabolic rate is the rate of energy expenditure / chemical activity in an organism. It can be measured by: oxygen consumption, carbon dioxide production, or heat (energy) released per unit time.

Compare the circulatory systems of fish, amphibians and mammals/birds in relation to metabolic rate.

Fish have a single circulatory system with a two-chambered heart. Amphibians and most reptiles have a three-chambered heart (incomplete double circulation). Birds and mammals have a four-chambered heart and complete double circulation, supporting the high metabolic rate needed for endothermy.

Distinguish between conformers and regulators in terms of internal environment and metabolic cost.

Conformers' internal environment changes with the external environment; they have low metabolic costs but a narrow range of ecological niches and must use behaviour to survive. Regulators control their internal environment by physiological homeostasis, which is energetically costly but allows a wider range of niches.

Explain negative feedback control using thermoregulation as an example.

Negative feedback reverses a change to restore the norm. If body temperature rises above the set point, the hypothalamus triggers vasodilation and sweating to lose heat; if it falls, vasoconstruction and shivering generate/retain heat, returning temperature to normal.

Compare dormancy types: what are predictive and consequential dormancy?

Predictive dormancy is triggered before adverse conditions arrive, in response to an external cue (e.g. shortening day length). Consequential dormancy begins after adverse conditions have set in. Predictive is more common in predictable environments.

Distinguish hibernation, aestivation and daily torpor as means of surviving adverse conditions.

Hibernation is dormancy with lowered metabolism to survive cold winters. Aestivation is dormancy to survive hot/dry summer conditions. Daily torpor is a short-term reduction in metabolic rate/activity over part of a 24-hour cycle, common in small mammals and birds with high metabolic rates.

Compare innate and learned behaviour in migration, and distinguish migration from extreme-condition avoidance.

Migration is the regular long-distance movement of animals to avoid adverse conditions (e.g. food shortage). It can be triggered innately (genetically inherited) or learned from experience. Migration is studied using long-term tracking such as leg/wing tags, satellite tracking and ringing.

Why are micro-organisms (e.g. bacteria, yeast) used to study environmental control of metabolism?

They have short generation times, can be grown in large numbers in a small space, and their metabolism is easily controlled and measured. This makes them ideal model organisms for research and biotechnology.

Describe the typical bacterial growth curve phases.

Lag phase (cells adjust, enzymes induced, little division); log/exponential phase (rapid division, conditions favourable); stationary phase (division equals death as nutrients deplete and toxins accumulate); death/decline phase (death exceeds reproduction).

Explain the difference between primary and secondary metabolites in micro-organisms.

Primary metabolites (e.g. for growth and reproduction) are produced during the log phase. Secondary metabolites (e.g. antibiotics) are produced in the stationary phase, often giving an ecological advantage when nutrients are scarce.

How are wild strains of micro-organisms improved for use in industry?

By mutagenesis (using mutagens to induce mutations) and selecting improved strains, by recombinant DNA technology (inserting genes), and by selective breeding/selection, to increase yield of useful products or remove unwanted ones.

Explain the relationship between food production, population growth and the need to increase yield sustainably.

The human population is rising, so food production must increase. This can be achieved by increasing the area of land cultivated or by increasing productivity per unit area through breeding, fertilisers and protection, ideally in sustainable ways that do not degrade the environment.

Why are most of the world's food crops produced from a small number of plant species?

A few plant species (e.g. cereals like wheat, rice, maize) are grown because they have a high yield, are easily cultivated, are nutritious and store well. Animals fed on plants lose energy at each trophic level, so growing plants for direct consumption is more energy-efficient.

Define gross primary productivity, net primary productivity and biological yield.

Gross primary productivity is the total energy fixed by plants in photosynthesis. Net primary productivity is the energy remaining after respiration ($\text{NPP} = \text{GPP} - \text{respiration}$). Biological yield is the total plant biomass; economic yield is the mass of the desired product (e.g. grain).

What are the limitations of photosynthesis that can be manipulated to increase crop yield?

Light intensity, carbon dioxide concentration and temperature limit the rate of photosynthesis. Yield can be improved by selecting crops with efficient light capture, optimum leaf area, and growing them in optimal conditions (e.g. greenhouses).

Distinguish field crops from glasshouse crops in terms of yield management.

Field crops are grown outdoors in large areas where conditions cannot be fully controlled; yield depends on weather, fertilisers and protection. Glasshouse crops are grown in enclosed environments where light, $\ce{CO2}$, temperature and water can be controlled to maximise yield, but at higher cost.

Explain inbreeding and the problem of inbreeding depression.

Inbreeding is breeding closely related individuals to produce a true-breeding (homozygous) population with desired characteristics. Repeated inbreeding can concentrate harmful recessive alleles, reducing fitness, fertility and yield, known as inbreeding depression.

What is cross-breeding and hybrid vigour (heterosis)?

Cross-breeding mates two different breeds/varieties. The resulting F1 hybrids can show hybrid vigour (heterosis): increased size, yield and vigour because favourable dominant alleles mask harmful recessives. F1 hybrids are uniform but not used for further breeding as the next generation varies.

Distinguish between cross-pollinating, self-pollinating and vegetatively propagated plants in breeding.

Cross-pollinators naturally outbreed; new combinations are made by crossing. Self-pollinators are naturally inbreeding and tend to be true-breeding. Vegetatively propagated plants produce genetically identical clones, allowing successful genotypes to be reproduced uniformly.

What is genetic transformation in crop improvement?

Single genes for desirable characteristics (e.g. pest resistance, herbicide tolerance) are inserted into the genome of a crop plant or animal using recombinant DNA technology, producing genetically modified (GM) organisms.

How are genetic markers used in selective breeding?

Genome sequencing identifies alleles linked to desirable characteristics. Organisms can be screened for these markers early in life, allowing breeders to select individuals with desired alleles without waiting to see the phenotype, speeding up breeding programmes.

Classify weeds, pests and diseases as the main competitors/threats to crops.

Weeds compete with crops for light, water and nutrients. Pests (e.g. insects, nematodes, molluscs) damage crops by feeding on them. Diseases are caused by fungi, bacteria and viruses, often spread by pests, reducing yield.

Distinguish annual weeds from perennial weeds and their competitive features.

Annual weeds have rapid growth, short life cycles and produce large numbers of seeds, often surviving as long-term seed banks. Perennial weeds have storage organs (allowing early-season growth) and reproduce vegetatively, making them persistent competitors.

Compare selective and systemic herbicides.

Selective herbicides kill certain plants (e.g. broad-leaved weeds) without harming the crop (e.g. narrow-leaved cereals). Systemic herbicides are absorbed and transported throughout the plant, killing it entirely including storage organs, useful against perennial weeds.

Distinguish contact, systemic and selective pesticides.

Contact pesticides kill on direct contact with the surface. Systemic pesticides are absorbed and spread through the plant/animal tissues. Selective pesticides target specific organisms. Each refers to how the chemical acts to control pests.

What problems are associated with the use of pesticides?

Pests can evolve resistance; pesticides may be toxic to non-target species and humans; persistent chemicals can bioaccumulate and biomagnify up food chains, harming top predators; and runoff can pollute ecosystems.

Define bioaccumulation and biomagnification.

Bioaccumulation is the build-up of a chemical (e.g. a pesticide) within an individual organism over time. Biomagnification is the increase in concentration of that chemical at successive trophic levels up a food chain, so top predators accumulate the highest concentrations.

What is biological control and integrated pest management (IPM)?

Biological control uses a natural predator, parasite or pathogen to control a pest population. IPM combines biological control, chemical control and cultural methods to manage pests effectively while minimising cost and environmental damage.

Give the costs and benefits of intensive (indoor) animal farming.

Benefits: high productivity, efficient use of food/energy, easy management, lower costs and prices. Costs: poor animal welfare (restricted movement, stress), higher disease risk requiring antibiotics, and ethical concerns; behavioural indicators of poor welfare may appear.

List the five categories of behavioural indicators used to assess poor animal welfare.

Stereotypy (repetitive, purposeless movements), misdirected behaviour (e.g. feather/hair pulling), failure in sexual or parental behaviour, altered levels of activity (very high hysteria or very low apathy), and abnormal/displacement behaviour.

What is imprinting and why is it important in animal behaviour?

Imprinting is a form of learning in which a young animal forms an attachment to the first large moving object it sees (usually the parent) during a sensitive critical period. It is important for following the parent, protection, and later mate recognition.

Distinguish habituation from other forms of learning.

Habituation is a simple form of learning in which an animal stops responding to a repeated stimulus that is neither beneficial nor harmful (e.g. ignoring a harmless sound). This conserves energy by not wasting responses on unimportant stimuli.

Define symbiosis, and distinguish mutualism from parasitism.

Symbiosis is a co-evolved intimate relationship between members of two different species. In mutualism both species benefit. In parasitism the parasite benefits while the host is harmed; parasites are often host-specific and have limited metabolism.

What is the difference between an endoparasite and an ectoparasite, and what is a vector?

Endoparasites live inside the host (e.g. tapeworms), ectoparasites live on the surface (e.g. fleas, ticks). A vector is an organism (often a secondary host) that transmits a parasite from one host to another.

Explain social hierarchy and its benefits in social animals.

A social hierarchy is a rank order within a group, often maintained by ritualistic threat and appeasement (submission) displays. Benefits include reduced energy-wasting aggression and serious injury, increased experienced animals' breeding success, and group stability.

What is cooperative hunting and how does it benefit social animals?

Cooperative hunting is when members of a social group hunt together. It allows larger prey to be caught, increases hunting success, requires less energy per individual, and means subordinate animals may gain more food than hunting alone.

Define altruism and kin selection in animal behaviour.

Altruism is behaviour that harms the donor (e.g. costs energy or risk) but benefits the recipient. Kin selection explains altruism towards relatives: helping relatives, who share genes, increases the donor's inclusive fitness by passing on shared alleles.

What are social insects and the roles of the castes in a colony?

Social insects (e.g. bees, ants, termites) live in colonies with a reproductive caste (queen and males) and a sterile worker caste. Workers cooperate to raise relatives, defend the colony and gather food, increasing the survival of shared genes (kin selection).

Define biodiversity and list its three components.

Biodiversity is the variety of life. Its components are: genetic diversity (variety of alleles within a population/species), species diversity (the number of different species and the relative abundance of each), and ecosystem diversity (variety of different ecosystems in an area).

Why is a population with low genetic diversity at greater risk of extinction?

Low genetic diversity means fewer alleles, so the population is less able to adapt to environmental change (e.g. disease, climate) through natural selection, increasing the risk of extinction. This often follows a population bottleneck or small population size.

What is a genetic bottleneck and its consequence for a species?

A bottleneck occurs when a population is sharply reduced (e.g. by hunting, disease or habitat loss), so the survivors carry only a fraction of the original genetic diversity. The recovered population has low genetic diversity and is vulnerable to further threats.

Explain how habitat fragmentation threatens biodiversity.

Fragmentation breaks a large habitat into smaller isolated patches, reducing population sizes and biodiversity. Increased edge effects degrade habitat quality, and isolation prevents interbreeding between fragments, lowering genetic diversity. Habitat corridors can reconnect fragments.

How do introduced (invasive, non-native) species threaten native biodiversity?

Introduced species may prey on, out-compete (for food/resources), hybridise with, or spread disease/parasites to native species that have no co-evolved defences. Naturalised invasive species spread rapidly and can cause native species decline or extinction.

State the relationship represented by the Simpson's diversity index and what high values indicate.

Simpson's diversity index combines species richness and the relative abundance (evenness) of each species. A community with many species in even proportions has high diversity and is generally more stable; one dominated by a few species has low diversity and lower resilience.

What is overexploitation and how does it threaten biodiversity?

Overexploitation is harvesting organisms (e.g. by overhunting or overfishing) faster than they can reproduce, reducing population sizes below recovery levels. It can drive species towards extinction and reduce both species and genetic diversity in ecosystems.