A2 Module 4

A2 Module 4
ENERGY, CONTROL AND

CONTINUITY

Introduction In this module the central role of ATP as the immediate provider

of energy for metabolic processes is covered. The biochemistry of

photosynthesis and respiration are studied in order to enable

understanding of how ATP is generated and how biological

compounds are synthesised. This module extends the work on

physiology and genetics that was undertaken in the Advanced

Subsidiary modules. It considers the ability of organisms to survive by maintaining a constant internal environment and responding to changes in the external environment. As well as studying examples of homeostasis, candidates survey a complete account of nervous communication from the stimulation of receptors, formation of nerve impulses and integration in the central nervous system to the response of effectors in the form of muscle contraction. The module explores how continuity of species is maintained by the transmission of genetic information from generation to generation, and how selection and evolution can account for the diversity of living organisms. The principles by which species are classified into groups using shared derived features are also covered.

This module covers part of the knowledge and understanding

specified in the mandatory subject criteria for Part 2 (A2) of an Advanced Level Biology syllabus, as set out in the document issued by QCA in June 1999. It covers sections 3.8, 3.13, 3.16, 3.17 and 3.18 of that document.

13.1 Energy supply

The relationship between Photosynthesis as a process in which light energy is used photosynthesis and in the

respiration synthesis of organic molecules.

Respiration as the process by which energy in organic molecules is made available for other processes within an organism.

ATP The synthesis of ATP from ADP and inorganic

phosphate, and its role as the immediate source of energy for biological processes.

13.2 Photosynthesis

Light-dependent reaction The light-dependent reaction only in sufficient detail to

show that:

light energy excites electrons in chlorophyll;

the energy from these excited electrons is used to generate ATP and reduced NADP;

photolysis of water makes hydrogen available for the light-independent reaction and gaseous oxygen is released.

Light-independent reaction The light-independent reaction only in sufficient detail to

show that:

carbon dioxide is accepted by ribulose bisphosphate to form two molecules of glycerate-3-phosphate;

ATP and reduced NADP are required for the reduction of glycerate-3-phosphate to carbohydrate;

ribulose bisphosphate is regenerated.

Chloroplast structure The structure and role of chloroplasts in relation to

photosynthesis.

13.3 Respiration

Glycolysis and Krebs cycle The biochemistry of aerobic respiration only in sufficient

detail to show that:

glycolysis involves the oxidation of glucose to pyruvate with a net gain of ATP and reduced NAD;

pyruvate combines with coenzyme A to produce acetylcoenzyme A;

acetylcoenzyme A is effectively a two-carbon molecule which combines with a four-carbon molecule to produce a six-carbon molecule which enters Krebs cycle;

Krebs cycle involves a series of oxidation reactions and the release of carbon dioxide leading to the production of ATP and reduced coenzyme (NAD or FAD);

synthesis of ATP is associated with the electron transport chain.

Mitochondria The structure and role of mitochondria in respiration.

13.4 Survival and coordination

Stimulus and response Organisms increase their chances of survival by

responding to changes in their environment.

Information is transferred in the nervous system through detection of stimuli by receptors and the initiation of a nerve impulse, leading to an associated response by effectors by means of a coordinator.

A simple reflex arc involving three neurones.

Information is transferred by hormones released by endocrine glands and affecting the physiological activities of target cells.

13.5 Homeostasis

Homeostasis Physiological control systems operate in mammals to

maintain a constant internal environment � this is homeostasis.

Negative feedback The principle of negative feedback and its role in

restoring systems to their original levels.

Regulation of body The processes involved in thermoregulation in a mammal, temperature including the role of thermoreceptors in the skin and the

hypothalamus.

Regulation of blood sugar The role of insulin and glucagon in the control of blood

sugar, including the importance of specific membrane receptors and their effect on enzyme-controlled reactions. The conversion of glucose to glycogen for storage.

Removal of metabolic waste Waste products of metabolism are frequently toxic and

must be removed from the body. Deamination of excess amino acids and the production of urea. (Details of the ornithine cycle not required.)

The processes involved in the formation of urine in the kidney, including ultrafiltration in the renal capsule and selective reabsorption in the proximal convoluted tubule.

Regulation of blood water The role of the loop of Henle in maintaining a gradient of potential ions across the medulla. The role of ADH in the control

of water by the distal convoluted tubule and the collecting duct.

The importance of the ionic gradient in regulating blood water potential.

13.6 Nervous coordination

The mammalian eye The structure and function of the iris in controlling the

amount of light which enters the eye.

The roles of the cornea, lens, ciliary muscles and suspensory ligaments in focusing an image on the retina.

Rods and cones The structure of rods and cones.

The photosensitive bleaching of rhodopsin in rods.

The trichromatic theory of colour vision as an explanation of the functioning of cones.

Differences in sensitivity and visual acuity as explained by differences in the distribution of rods and cones and the connections they make with neurones in the optic nerve.

The nerve impulse The structure of a myelinated motor neurone.

The establishment of a resting potential in terms of the differential membrane permeability and the presence of cation pumps.

The initiation of an action potential and its all-or-nothing nature, explained by changes in membrane permeability leading to deplorisation.

The passage of an action potential along non-myelinated and myelinated axons resulting in nerve impulses.

The nature and importance of the refractory period in producing discrete nerve impulses.

Synapses and synaptic The detailed structure of a synapse as revealed by an transmission electron microscope.

The sequence of events involved in the action of a cholinergic synapse and a neuromuscular junction.

Drugs and synapses The effect of drugs on synaptic transmission.

When provided with information, candidates should be able to

predict and explain the effects of specific drugs on a synapse.

(Candidates will not be required to recall the effects of individual drugs.)

13.7 Analysis and integration

The brain and cerebral The principal functions of the cerebral hemispheres:

hemispheres

the role of sensory areas in receiving input from receptors and motor areas controlling effectors;

the relationship between the size of the relevant part of the cerebral hemispheres and the complexity of innervation;

the control of one side of the body by the opposite hemisphere;

the role of association areas in interpreting sensory input as illustrated by the visual association area;

the location and role of areas of the cerebral hemispheres associated with speech.

The autonomic nervous The general role of the sympathetic and parasympathetic system components of the autonomic nervous system.

The specific effects of the autonomic nervous system on controlling:

pupil diameter and tear production in the eye;

the emptying of the bladder.

13.8 Muscles are effectors

which enable movement to

be carried out

Antagonistic muscle action Candidates should be able to explain examples of

movement in terms of antagonistic muscle action.

Muscle structure The structure of skeletal muscle as seen with light and

electron microscopes.

The relationship between the structure of a sarcomere and the distribution of actin and myosin.

Muscle contraction The sliding filament hypothesis of muscle contraction.

The role of tropomyosin, calcium ions and ATP in the cycle of actomyosin bridge formation.

Candidates should be able to relate the mechanism of muscle contraction to the appearance of a sarcomere in a contracted or a relaxed state.

13.9 Inheritance

Genotype The genotype is the genetic constitution of an organism.

The expression of this genetic constitution and its interaction with the environment is the phenotype.

The alleles at a specific locus may be either homozygous or heterozygous. Alleles may be dominant, recessive or codominant.

There may be multiple alleles of a single gene.

Meiosis and fertilisation The principal events associated with meiosis, to include:

pairing by homologous chromosomes;

formation of bivalents;

chiasma formation and exchange between chromatids;

separation of chromatids;

production of haploid cells.

Candidates should be able to explain:

the behaviour of alleles and homologous chromosomes during meiosis and fertilisation, i.e. independent assortment during meiosis and random recombination during fertilisation;

the random movement of non-homologous chromosomes and non allelic genes.

(Details and names of individual stages of meiosis are not required.)

Sex determination The genetic basis of sex determination.

Monohybrid and dihybrid Candidates should be able to apply the above inheritance principles to interpret and use fully annotated genetic

diagrams to predict the results of:

monohybrid crosses involving dominant, recessive and codominant alleles;

crosses involving sex-linked characteristics;

dihybrid crosses, including epistasis.

(Predictions involving linkage on autosomes are not required.)

13.10 Variation

Types of variation Variation between individuals may be either continuous

or discontinuous.

Causes of variation Similarities and differences between individuals within a

species may be the result of genetic factors, differences in environmental factors, or a combination of both.

Candidates should be able to interpret data to determine the relative effects of genetic and environmental factors involved in continuous and discontinuous variation.

Candidates should be able to explain how crossing over, independent assortment of chromosomes, random fusion of gametes and mutation contribute to genetic variation.

13.11 Selection and evolution

Natural selection Individuals within a species may show a wide range of

variation.

Predation, disease and competition result in differential survival and reproduction. Those organisms with a selective advantage are more likely to survive, reproduce and pass on their genes to the next generation.

Candidates should be able to:

use specific examples to explain how natural selection produces changes within a species;

interpret data and use unfamiliar information to explain how natural selection produces change within a population.

Speciation The concept of the species in terms of production of

fertile offspring.

Candidates should be able to explain:

how natural selection and isolation may result in changes in the allele and phenotype frequency and lead to the formation of a new species;

how evolutionary change over a long period of time has resulted in a great diversity of forms among living organisms.

13.14 Classification

Principles of taxonomy The principles and importance of taxonomy.

A classification system comprises a hierarchy in which groups are contained within larger composite groups with no overlap.

The phylogenetic groupings are based on patterns of evolutionary history.

The five kingdoms One hierarchy comprises Kingdom, Phylum, Class,

Order, Family, Genus, Species.

The distinguishing features of the five kingdoms � prokaryotes, protoctists, fungi, plants and animals.