Category: Biology

Biological Molecules

You will get to grips with the very basic molecules of life. Each quiz takes you through the structure of each monomer, the structural differences between them, and how they join together to become biological polymers.

We start with Carbohydrate Structure, looking first at the Monosaccharides;Alpha and Beta Glucose, and how through condensation reactions, they can be joined together by glycosidic bonds to make disaccharides. From here we test your knowledge of the structural differences, and resulting differences in the properties of the polysaccharides : Amylose, Amylo-pectin, Cellulose and Glycogen.

Lipid structure, and the structural differences between saturated and unsaturated fatty acids is tested here along with Ester linkages ( or bonds).

Protein structure again starts with the monomers; Amino Acids. The quiz tests your knowledge of the carboxyl group and the amino group, and the differing R groups. It tests your ability to identify a peptide bond, and how the order of amino acids dictates the ensuing secondary, tertiary and quaternary structures of proteins.There are two quizzes on Enzymes, and what factors affect enzyme function In these quizzes you will apply your knowledge of protein structure and be able to interpret graphs.

The structure of DNA ( and its single stranded relative RNA) is also tested in this unit; looking at Nucleotide structure, and phosphodiester bonds. In this unit there is also a quiz looking at the fine detail of DNA replication; understanding the role of each enzyme, where it attaches, and which direction it moves in. You are also tested on the evidence of Semi Conservative Replication.

Lastly there is a quiz testing your understanding of the role of inorganic ions such as sodium and phosphate. Building up to the structure and role of ATP. The importance of water is the last little section in this quiz , finishing off knowledge which will support every aspect of your A Level understanding from now on.

Biological Molecules

Cells

In this unit of A Level Biology: Cells, we start by testing your knowledge of Eukaryotic Organelles. Extending on from the basics learnt at GCSE, this quiz expects you to be able to identify and give the detailed function from the familiar Nucleus, through to the newly introduced Golgi Body and Smooth Endoplasmic Reticulum.

The next quiz then looks at Prokaryotic structure. Focusing predominantly on Bacteria, this quiz looks at the differences between Prokaryotes and Eukaryotes; particularly looking at DNA and Binary Fission.

Your mathematical skill is tested in Magnification , with your ability to convert units, understand Order of Magnitude, and work out the magnification and Actual size of images shown. Following on from this, Microscopes and Fractionation tests your understanding of the difference between Scanning and Transmission Electron microscopes. It also, applies your knowledge of the technique of Cell fractionation, where centrifugation at different speeds is used to separate out organelles.

Eukaryotic Cell division is tested in the Mitosis quiz. Where you need to be able identify Prophase, Metaphase, Anaphase and Telophase. You also need to understand the role of Interphase in the Cell Cycle.

Two quizzes are dedicated to the Plasma Membrane. You will need to know the structure of the Phosopholipid Bilayer,and how that relates to function. How different molecules can pass across the Membrane, is also tested and again links into other units further on in A Level Biology.

Lastly we look at the Immune response : both the cellular response via T cells, and the Humoral response via B cells. The role of antibodies is tested both with in the Immune Response, but also in a second quiz on Monoclonal Antibodies.

Cells

Exchanges of Substances with the Environment

In this unit we get our first taste of Physiology in A Level biology – and start to look at how the body functions and systems with-in organisms.

We pick up from GCSE looking at Surface Area to Volume ratio, and adaptations of this that allow organisms to survive; for example, at different temperatures. Surface area also links into the gaseous exchange systems in humans, insects, fish and plants. Understanding of the human gaseous exchange system also requires understanding and interpreting data on diseases which affect it.

Mass Transport means the movement of substances around a multicellular organism. In many organisms this takes the form of a circulatory system. In this unit, we look at Haemoglobin, and oxygen dissociation curves. You need to be able to describe the effect of partial pressure of oxygen on haemogoblin’s affinity for oxygen. You also need to be able to describe the Bohr effect, and apply your knowledge to what may be unfamiliar species such as lugworms.

In terms of gross anatomy, at A level several major arteries such as the aorta, pulmonary and renal arteries need to be identified, and more importantly the structural differences between arteries, veins and capillaries. The structures of the heart also need to be identified, all be it in much the same level as higher GCSE. The cardiac cycle is extended from GCSE, looking at interpreting pressure changes , and calculating cardiac output and stroke volume. Cardiovascular disease data must be interpreted, including; atheroma, and thrombus formation.

Mass transport in plants has two separate routes:transpiration for water via xylem, and mass flow for organic substances via phloem. Once again, GCSE is extended to looking at cohesion -tension in the xylem, and translocation via mass flow hypothesis in plants. In the Mass Flow Hypothesis, changes in water potential caused by the formation of soluble substances (like glucose) cause pressure changes, which push the solutes towards ‘sinks’ where the solute concentration is lowered.

Exchanges of Substances with the Environment

Genetic Variation and Information

In this unit, we start off with DNA and RNA as the genetic molecules from unit 1, this time identifying differences between prokaryotic and eukaryotic DNA, and chromosome structure. Extending from GCSE, we look at protein synthesis and the process of transcription. This is the use of RNA polymerase to make complementary pre-mRNA from a coding section of DNA. The pre-mRNA contains introns, which are then spliced out to form the shorter mRNA. Translation then occurs in the ribosome. Here, we meet a new clover shaped polynucleotide : transfer RNA. tRNA has anticodons on the bottom loop, complementary to the codons on the mRNA, and specific amino acids on the top. The ribosome has space for 3 tRNA.s to dock, and join together the amino acids to form a polypeptide.

Genetic variation can occur due to mutation or meiosis. A few simple mutations to the base sequence of DNA are discussed here ( there are more in Unit 8), along with independent segregation and ‘crossing over’ of chromatids in the first phases of meiosis. This genetic variation is then applied to Natural Selection. Students need to be able to differentiate between directional and stabilising selection.

Phylogenetic classification uses evolutionary origins as a way of grouping organisms into a hierarchy. The different organisms can be grouped by biochemical similarity . The most obvious of this is the sequence of DNA, which is obviously linked to the primary structure of key proteins.

In this unit, students are also expected to develop maths skills , including calculation of means and standard deviation, and understanding what standard deviation represents. Although, standard deviation will not be need to be calculated in the AQA exam.

Genetic Variation & Information

The Transfer of Energy

Life depends on continuous transfers of energy.

In this unit we start with photosynthesis. Splitting it into the light dependent reactions (LDR), and the Light Independent reactions (LIR).

LDR take place in the thylakoid membranes of the chloroplasts. Light energy is absorbed by chlorophyll, and results in electron transfer, which in turn creates a proton gradient, and the enzyme ATP synthase to produce ATP. The LDR also produces reduced NADP, which together with carbon dioxide enter the Calvin cycle and produce triose phosphate which can be converted to other organic molecules such as glucose. There are also three required practicals on the cross board CPAC linked to photosynthesis.

In aerobic respiration, the breakdown of glucose as a respiratory substrate starts with glycolysis in the cytoplasm, which then links to the mitochondria. Krebs cycle occurs in the mitochondrial matrix, finishing off with the Electron Transport Chain producing ATP.

This unit extends to the transfer of energy between organisms, as Net Primary Productivity (NPP) . this is Gross Primary Productivity ( GPP) minus respiratory losses. This extends to animals ( consumers) when N ( Net production) is equal to chemical energy ingested, minus losses in faeces, urine and respiration. Farming practices are designed to make these transfers most efficient.

Finally, nutrients alo cycle through the ecosystem, and at A Level biology , these focus on the Nitrogen cycle and the Phosphorus cycle. This is extended to A level by the role of saprobionts and mycorrhizae.

The Transfer of Energy

Responding to Change

A stimulus is a change in the internal or external environment, which can be detected by a receptor, and an effect brought about by an effector. In this unit, we look at how different organisms detect and coordinate these responses.

Plants respond to stimuli via growth factors. At A Level, this is based around Indole Acetic Acid (IAA). the responses are slow, growth responses called tropisms. There have been many experiments on plant responses, and some of these are tested in here.

Animals ( such as many invertebrates) can have simple responses to stimuli that can enable a motile organism, to move to a favourable environment. These are either taxes , which are directional responses, or kineses, which are non-directional responses.

Nervous coordination includes the establishment and maintenance of a negative resting potential,and the generation of an action potential due to changes in membrane permeability to sodium and potassium ions. Once again, we extend GCSE basic understanding of synapses, to consider summation and inhibition too. Receptors are cells that detect specific stimuli, and cause the establishment of a generator potential. In a pacinian corpuscle, the stimulus is pressure. We also use the examples of rod and cone cells as receptors that detect light.

Skeletal muscle is an effector. The arrival of an action potential causes biochemical changes which results in cycles of actinomyosin bridge breaking and formation.

Homeostasis is the maintenance of a constant internal environment. Specifically we look at the control of blood glucose via insulin and glucagon. Also the action of adrenaline, and the second messenger model. We also look specifically at the control of water potential of the blood via ADH on the kidney.

Responding to Change

Populations, Evolutions and Genetics

All individuals of a population show variation in their phenotype, caused by the environment and genetics. In this unit, we look at mendelian ratios derived from monohybrid and dihybrid crosses. We also look at sex linkage, autosomal linkage and epistasis.

The Hardy Weinberg equation is a quadratic equation which allows us to calculate allele frequency in a population. The Hardy Weinberg equation assumes a population to be large, with random mating, and no immigration, no emigration, no mutation . To use the Hardy Weinberg, you must first identify what is the recessive allele, and then if the information on that allele is about whole organisms ( in which case use ‘q²’) or number of alleles in which case use ‘q’. Variations due to meiosis and mutation, and ensuing differential reproductive success give rise to new alleles and changes in allele frequency.

This can lead to evolution of new species, called speciation. Speciation can be either allopatric ( geographically separated) or sympatric (reproductively isolated without geographical barriers). This unit also looks at the study of populations in ecosystems. Here we recap terms such as ‘community’ and ‘niche’ and interspecific and intraspecific speciation.

Techniques such as random sampling, belt transects and mark-release-recapture are also covered here. Succession is the process where an ecosystem changes overtime ( this is not the same process as evolution). Pioneer species ( often lichen) are the first species to grow on bare rock, creating a thin soil, so bigger species are then able to take root. Lastly conservation is also covered in this unit.

Populations, Evolutions & Genetics

Control of Expression

Although all cells within an organism carry the same genetic code, different parts of the code can be ‘turned on’ , and used by different cells. This ‘turning on’ of genes is called gene expression. It is the different expression of genes which allows cells to have different features and functions.

Mutations are re-visited in this unit ( also in unit 4) , but extended to look at inversion, duplication and translocation of bases. Some mutations will lead to a change in the entire reading frame after that point, and this is called a frame shift. Mutation of tumour suppressor genes and proto-oncogenes can lead to cancer.

Cancer can also be influenced by epigenetics. Epigenetics is the marking of DNA or histone proteins, which affects the likelihood of that section of DNA being expressed or not. Epigenetic control is perhaps the biggest discovery this century in the field of Biology. The marks are in the form of acetylation or methylation, and have been found to have strong roles in disease states such as cancer.

Another recent discovery in the control of expression has been the discovery of Small Interfering RNAs ( siRNA) . Here RNAs bind to mRNA’s causing them to be degraded by enzymes, and therefore preventing that mRNA from being translated.

Gene technologies are ever advancing, and this is taken into account with the acknowledgement that sequencing methods for example are constantly improving . Recombinant DNA technologies are revisited from GCSE, and advanced by looking at the Polymerase Chain Reaction ( PCR) as a method of in vitro DNA replication. The use of DNA probes and hybridisation, along with genetic finger-printing are also included in this section.

Control of Expression

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