AS Level Biology Notes
11 units
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24 lessons
AS Level Biology is the first half of the A Level Biology curriculum, typically studied by students in the UK and some international schools as part of their post-16 education. The AS Level course provides a foundational understanding of biological concepts and is generally taken in the first year of A Levels, with students either progressing to the full A Level in the second year or stopping at the AS qualification.
Key Components of AS Level Biology
- Cell Structure: Studying the structure and function of eukaryotic and prokaryotic cells, including cellular organelles.
- Biological Molecules: Understanding macromolecules like proteins, carbohydrates, lipids, and nucleic acids and their roles in living organisms.
- Enzymes: Learning how enzymes work, enzyme kinetics, and factors affecting enzyme activity.
- Exchange and Transport: Covering gas exchange, circulatory systems, and transport mechanisms in plants and animals.
- Genetics and Variation: Exploring basic genetics, DNA, inheritance patterns, and genetic variation.
Skills Developed
- Experimental Techniques: Performing and interpreting experiments, with emphasis on lab work and scientific method.
- Data Analysis: Interpreting and analyzing biological data, often presented in graphs, charts, or tables.
- Critical Thinking: Applying knowledge to unfamiliar contexts and developing problem-solving skills.
AS Level Biology assessments are usually a mix of written exams, which include multiple-choice, short-answer, and long-answer questions. This qualification is a stepping stone for careers and further studies in biology, medicine, environmental science, and biotechnology.
Candidates for Cambridge International AS Level Biology study the following topics:
- Cell structure
- Biological molecules
- Enzymes
- Cell membranes and transport
- The mitotic cell cycle
- Nucleic acids and protein synthesis
- Transport in plants
- Transport in mammals
- Gas exchange
- Infectious diseases
- Immunity
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- 1.1.1 Study of Aspergillus by using Temporary Mount Technique
- 1.1.2 Study of Penicillium using Temporary Mount
- 1.1.3 Study of Rhizopus by using Temporary Mount
- 1.1.4 Stomata Under Microscope – Temporary Mount Technique
- 1.1.5 Temporary Wet Mount (TWM) technique for observation of Living Organisms.
- 1.1.6 Temporary Dry Mount Slides Preparation Procedure
- 1.1.7 calculate magnifications of images and actual sizes of specimens from drawings, photomicrographs and electron micrographs (scanning and transmission)
- 1.1.8 use an eyepiece graticule and stage micrometer scale to make measurements and use the appropriate units, millimetre (mm), micrometre (µm) and nanometre (nm)
- 1.1.9 define resolution and magnification and explain the differences between these terms, with reference to light microscopy and electron microscopy
- 1.1.10 draw cells from microscope slides and photomicrographs
- 1.1.11 Stage Micrometer – Definition, Principle, Parts, Procedure, Applications
- 1.1.12 How to calibrate a Microscope With a Stage Micrometer?
- 1.1.13 Ocular Micrometer – Definition, Principle, Parts, Applications
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- 1.2.1 Cell membrane (Plasma Membrane) Structures and Functions
- 1.2.2 nucleus, nuclear envelope and nucleolus
- 1.2.3 rough endoplasmic reticulum
- 1.2.4 smooth endoplasmic reticulum
- 1.2.5 Golgi body (Golgi apparatus or Golgi complex)
- 1.2.6 mitochondria
- 1.2.7 ribosomes
- 1.2.8 Prokaryotic Ribosomes
- 1.2.9 centrioles
- 1.2.10 cilia
- 1.2.11 microvilli
- 1.2.12 chloroplasts
- 1.2.13 cell wall
- 1.2.14 plasmodesmata
- 1.2.15 vacuole
- 1.2.16 lysosomes
- 1.2.17 microtubules
- 1.2.18 outline key structural features of a prokaryotic cell as found in a typical bacterium, including: • unicellular • generally 1–5 µm diameter • peptidoglycan cell walls • circular DNA • 70S ribosomes • absence of organelles surrounded by double membranes
- 1.2.19 compare the structure of a prokaryotic cell as found in a typical bacterium with the structures of typical eukaryotic cells in plants and animals
- 1.2.20 state that all viruses are non-cellular structures with a nucleic acid core (either DNA or RNA) and a capsid made of protein, and that some viruses have an outer envelope made of phospholipids
- 1.2.21 Sandwich (Davson–Danielli) model of cell membrane
- 1.2.22 Rough vs Smooth Endoplasmic Reticulum
- 1.2.23 Mitochondrial DNA (mtDNA) – Structure, Replication Mechanism, Factors
- 1.2.24 Differences Between Mitochondria and Chloroplast
- 1.2.25 compare the structure of typical plant and animal cells
- 1.2.26 state that cells use ATP from respiration for energy-requiring processes
- 1.2.27 Vacuole Staining – Observation of Vacuoles under Microscope
- 1.2.28 Food Vacuole – Definition, Types, Formation, Structure, Functions
- 1.2.29 Difference between Cilia and Microvilli
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- 2.1.1 the Benedict’s test for reducing sugars
- 2.1.2 the iodine test for starch
- 2.1.3 the emulsion test for lipids
- 2.1.4 the biuret test for proteins
- 2.1.5 describe and carry out a test to identify the presence of non-reducing sugars, using acid hydrolysis and Benedict’s solution
- 2.1.6 describe and carry out a semi-quantitative Benedict’s test on a reducing sugar solution by standardising the test and using the results (time to first colour change or comparison to colour standards) to estimate the concentration
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- 2.2.1 describe and draw the ring forms of α-glucose and β-glucose
- 2.2.2 define the terms monomer, polymer, macromolecule, monosaccharide, disaccharide and polysaccharide
- 2.2.3 state the role of covalent bonds in joining smaller molecules together to form polymers
- 2.2.4 state that glucose, fructose and maltose are reducing sugars and that sucrose is a non-reducing sugar
- 2.2.5 describe the formation of a glycosidic bond by condensation, with reference to disaccharides, including sucrose, and polysaccharides
- 2.2.6 describe the breakage of a glycosidic bond in polysaccharides and disaccharides by hydrolysis, with reference to the non-reducing sugar test
- 2.2.7 describe the molecular structure of the polysaccharides starch (amylose and amylopectin) and glycogen and relate their structures to their functions in living organisms
- 2.2.8 describe the molecular structure of the polysaccharide cellulose and outline how the arrangement of cellulose molecules contributes to the function of plant cell walls
- 2.2.9 state that triglycerides are non-polar hydrophobic molecules and describe the molecular structure of triglycerides with reference to fatty acids (saturated and unsaturated), glycerol and the formation of ester bonds
- 2.2.10 relate the molecular structure of triglycerides to their functions in living organisms
- 2.2.11 describe the molecular structure of phospholipids with reference to their hydrophilic (polar) phosphate heads and hydrophobic (non-polar) fatty acid tails
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- 2.3.1 describe and draw the general structure of an amino acid
- 2.3.2 describe the formation and breakage of a peptide bond
- 2.3.3 describe the types of interaction that hold protein molecules in shape: hydrophobic interactions, hydrogen bonding, ionic bonding, covalent bonding, including disulfide bonds
- 2.3.4 state that globular proteins are generally soluble and have physiological roles and fibrous proteins are generally insoluble and have structural roles
- 2.3.5 describe the structure of a molecule of haemoglobin as an example of a globular protein, including the formation of its quaternary structure from two alpha (α) chains (α–globin), two beta (β) chains (β–globin) and a haem group
- 2.3.6 relate the structure of haemoglobin to its function, including the importance of iron in the haem group
- 2.3.7 describe the structure of a molecule of collagen as an example of a fibrous protein, and the arrangement of collagen molecules to form collagen fibres
- 2.3.8 relate the structures of collagen molecules and collagen fibres to their function
- 2.3.9 explain the meaning of the terms primary structure, secondary structure, tertiary structure and quaternary structure of proteins
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- 3.1.1 state that enzymes are globular proteins that catalyse reactions inside cells (intracellular enzymes) or are secreted to catalyse reactions outside cells (extracellular enzymes)
- 3.1.2 explain the mode of action of enzymes in terms of an active site, enzyme–substrate complex, lowering of activation energy and enzyme specificity,
- 3.1.3 investigate the progress of enzyme-catalysed reactions by measuring rates of formation of products using catalase and rates of disappearance of substrate using amylase
- 3.1.4 outline the use of a colorimeter for measuring the progress of enzyme-catalysed reactions that involve colour changes
- 3.1.5 Active Site For Enzymes – Definition, Features, Mechanism, Example
- 3.1.6 The Lock and Key Model
- 3.1.7 The Induced Fit Model
- 3.1.8 Conformational selection hypothesis
- 3.1.9 Colorimeter vs Spectrophotometer
- 3.1.10 Enzyme Inhibition – Definition, Types, Mechanism, Examples
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- 3.2.1 investigate and explain the effects of the following factors on the rate of enzyme-catalysed reactions: temperature, pH (using buffer solutions), enzyme concentration, substrate concentration, inhibitor concentration
- 3.2.2 explain that the maximum rate of reaction (Vmax) is used to derive the Michaelis–Menten constant (Km), which is used to compare the affinity of different enzymes for their substrates
- 3.2.3 explain the effects of reversible inhibitors, both competitive and non-competitive, on enzyme activity
- 3.2.4 Enzyme Immobilization – Definition, Methods, Advantages, Disadvantages
- 3.2.5 investigate the difference in activity between an enzyme immobilised in alginate and the same enzyme free in solution, and state the advantages of using immobilised enzymes
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- 4.1.1 describe the fluid mosaic model of membrane structure with reference to the hydrophobic and hydrophilic interactions that account for the formation of the phospholipid bilayer and the arrangement of proteins
- 4.1.2 describe the arrangement of cholesterol, glycolipids and glycoproteins in cell surface membranes
- 4.1.3 describe the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in cell surface membranes, with reference to stability, fluidity, permeability, transport (carrier proteins and channel proteins), cell signalling (cell surface receptors) and cell recognition (cell surface antigens)
- 4.1.4 outline the main stages in the process of cell signalling leading to specific responses: • secretion of specific chemicals (ligands) from cells • transport of ligands to target cells • binding of ligands to cell surface receptors on target cells
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- 4.2.1 simple diffusion
- 4.2.2 facilitated diffusion
- 4.2.3 osmosis
- 4.2.4 active transport
- 4.2.5 endocytosis
- 4.2.6 exocytosis
- 4.2.7 investigate simple diffusion and osmosis using plant tissue and non-living materials, including dialysis (Visking) tubing and agar
- 4.2.8 illustrate the principle that surface area to volume ratios decrease with increasing size by calculating surface areas and volumes of simple 3-D shapes (as shown in the Mathematical requirements)
- 4.2.9 investigate the effect of changing surface area to volume ratio on diffusion using agar blocks of different sizes
- 4.2.10 investigate the effects of immersing plant tissues in solutions of different water potentials, using the results to estimate the water potential of the tissues
- 4.2.11 explain the movement of water between cells and solutions in terms of water potential and explain the different effects of the movement of water on plant cells and animal cells (knowledge of solute potential and pressure potential is not expected)
- 4.2.12 Difference Between Simple Diffusion and Facilitated Diffusion
- 4.2.13 Facilitated Diffusion vs Active transport
- 4.2.14 Difference Between endocytosis and exocytosis
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- 5.1.1 describe the structure of a chromosome, limited to: DNA, histone proteins, sister chromatids, centromere, telomeres
- 5.1.2 explain the importance of mitosis in the production of genetically identical daughter cells during: growth of multicellular organisms replacement of damaged or dead cells, repair of tissues by cell replacement, asexual reproduction
- 5.1.3 outline the Cell cycle
- 5.1.4 mitosis
- 5.1.5 cytokinesis
- 5.1.6 Meiosis
- 5.1.7 Checkpoints in the Cell Cycle – G1, G2, Metaphase (Spindle) Checkpoints
- 5.1.8 outline the role of telomeres in preventing the loss of genes from the ends of chromosomes during DNA replication
- 5.1.9 explain how uncontrolled cell division can result in the formation of a tumour
- 5.1.10 outline the role of stem cells in cell replacement and tissue repair by mitosis
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- 5.2.1 describe the behaviour of chromosomes in plant and animal cells during the mitotic cell cycle and the associated behaviour of the nuclear envelope, the cell surface membrane and the spindle (names of the main stages of mitosis are expected: prophase, metaphase, anaphase and telophase
- 5.2.2 interpret photomicrographs, diagrams and microscope slides of cells in different stages of the mitotic cell cycle and identify the main stages of mitosis
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- 6.1.1 describe the structure of nucleotides, including the phosphorylated nucleotide ATP (structural formulae are not expected)
- 6.1.2 Nucleotides and Nucleosides
- 6.1.3 describe the structure of a DNA molecule as a double helix
- 6.1.4 describe the semi-conservative replication of DNA during the S phase of the cell cycle
- 6.1.5 describe the structure of an RNA molecule, using the example of messenger RNA (mRNA)
- 6.1.6 state that the bases adenine and guanine are purines with a double ring structure, and that the bases cytosine, thymine and uracil are pyrimidines with a single ring structure (structural formulae for bases are not expected)
- 6.1.7 describe the importance of complementary base pairing between the 5′ to 3′ strand and the 3′ to 5′ strand (antiparallel strands)
- 6.1.8 differences in hydrogen bonding between C–G and A–T base pairs
- 6.1.9 describe the linking of nucleotides by phosphodiester bonds
- 6.1.10 describe the differences between leading strand and lagging strand replication as a consequence of DNA polymerase adding nucleotides only in a 5′ to 3′ direction
- 6.1.11 DNA polymerase
- 6.1.12 DNA ligase
- 6.1.13 Structure of messenger RNA (mRNA)
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- 6.2.1 Protein Synthesis (Translation)- Definition, Steps, Sites, Machinery
- 6.2.2 describe the principle of the universal genetic code in which different triplets of DNA bases either code for specific amino acids or correspond to start and stop codons
- 6.2.3 describe how the information in DNA is used during transcription and translation to construct polypeptides, including the roles of: • RNA polymerase • messenger RNA (mRNA) • codons • transfer RNA (tRNA) • anticodons • ribosomes
- 6.2.4 state that the strand of a DNA molecule that is used in transcription is called the transcribed or template strand and that the other strand is called the non-transcribed strand
- 6.2.5 explain that, in eukaryotes, the RNA molecule formed following transcription (primary transcript) is modified by the removal of non-coding sequences (introns) and the joining together of coding sequences (exons) to form mRNA
- 6.2.6 state that a gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
- 6.2.7 explain that a gene mutation is a result of substitution or deletion or insertion of nucleotides in DNA and outline how each of these types of mutation may affect the polypeptide produced
- 6.2.8 state that a polypeptide is coded for by a gene and that a gene is a sequence of nucleotides that forms part of a DNA molecule
- 6.2.9 Mechanisms of Protein Synthesis Regulation in Prokaryotic Cells
- 6.2.10 Mechanisms of Protein Synthesis Regulation in Eukaryotes Cells
- 6.2.11 Translation In Eukaryotes – Protein synthesis in Eukaryotic
- 6.2.12 Protein Synthesis Inhibitors – Definition, Mechanism, Examples
- 6.2.13 Anticodon – Definition, Principle, Functions, Examples
- 6.2.14 Codon Chart and Codon Table
- 6.2.15 Characteristic of Genetic Code
- 6.2.16 Genetic Code – Definition, Characteristics, Wobble Hypothesis
- 6.2.17 RNA Polymerase – Structure, Definition, Types, and Functions
- 6.2.18 messenger RNA (mRNA)
- 6.2.19 Transfer-messenger RNA (tmRNA) – Definition, Structure, Properties
- 6.2.20 tRNA – Structure, Definition, Functions, Types
- 6.2.21 Ribosome – Types, Structure, Function, and Diagram
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- 7.1.1 Xylem Parenchyma – Definition, Structure, Types, Functions
- 7.1.2 Difference Between Xylem and Phloem
- 7.1.3 draw and label xylem vessel elements, phloem sieve tube elements and companion cells from microscope slides, photomicrographs and electron micrographs
- 7.1.4 relate the structure of xylem vessel elements, phloem sieve tube elements and companion cells to their functions
- 7.1.5 draw plan diagrams of transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants from microscope slides and photomicrographs
- 7.1.6 describe the distribution of xylem and phloem in transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants
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- 7.2.1 state that some mineral ions and organic compounds can be transported within plants dissolved in water
- 7.2.2 describe the transport of water from the soil to the xylem through the: • apoplast pathway, including reference to lignin and cellulose • symplast pathway, including reference to the endodermis, Casparian strip and suberin
- 7.2.3 explain that transpiration involves the evaporation of water from the internal surfaces of leaves followed by diffusion of water vapour to the atmosphere
- 7.2.4 explain how hydrogen bonding of water molecules is involved with movement of water in the xylem by cohesion-tension in transpiration pull and by adhesion to cellulose in cell walls
- 7.2.5 make annotated drawings of transverse sections of leaves from xerophytic plants to explain how they are adapted to reduce water loss by transpiration
- 7.2.6 state that assimilates dissolved in water, such as sucrose and amino acids, move from sources to sinks in phloem sieve tubes
- 7.2.7 explain how companion cells transfer assimilates to phloem sieve tubes, with reference to proton pumps and cotransporter proteins
- 7.2.8 explain mass flow in phloem sieve tubes down a hydrostatic pressure gradient from source to sink
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- 8.1.1 state that the mammalian circulatory system is a closed double circulation consisting of a heart, blood and blood vessels including arteries, arterioles, capillaries, venules and veins
- 8.1.2 describe the functions of the main blood vessels of the pulmonary and systemic circulations, limited to pulmonary artery, pulmonary vein, aorta and vena cava
- 8.1.3 recognise arteries, veins and capillaries from microscope slides, photomicrographs and electron micrographs and make plan diagrams showing the structure of arteries and veins in transverse section (TS) and longitudinal section (LS)
- 8.1.4 explain how the structure of muscular arteries, elastic arteries, veins and capillaries are each related to their functions
- 8.1.5 recognise and draw red blood cells, monocytes, neutrophils and lymphocytes from microscope slides, photomicrographs and electron micrographs
- 8.1.6 state that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, limited to solvent action and high specific heat capacity
- 8.1.7 state the functions of tissue fluid and describe the formation of tissue fluid in a capillary network
- 8.1.8 Human Heart – Definition, Location, Anatomy, Structure, Functions
- 8.1.9 Conducting System of Heart Beat
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- 8.2.1 describe the role of red blood cells in transporting oxygen and carbon dioxide with reference to the roles of: • haemoglobin • carbonic anhydrase • the formation of haemoglobinic acid • the formation of carbaminohaemoglobin
- 8.2.2 describe the chloride shift and explain the importance of the chloride shift
- 8.2.3 describe the role of plasma in the transport of carbon dioxide
- 8.2.4 describe and explain the oxygen dissociation curve of adult haemoglobin
- 8.2.5 explain the importance of the oxygen dissociation curve at partial pressures of oxygen in the lungs and in respiring tissues
- 8.2.6 describe the Bohr shift and explain the importance of the Bohr shift
- 8.2.7 Hemoglobin – Definition, Structure and Function
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- 8.3.1 describe the external and internal structure of the mammalian heart
- 8.3.2 explain the differences in the thickness of the walls of the: • atria and ventricles • left ventricle and right ventricle
- 8.3.3 describe the cardiac cycle, with reference to the relationship between blood pressure changes during systole and diastole and the opening and closing of valves
- 8.3.4 explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne tissue in the cardiac cycle (knowledge of nervous and hormonal control is not expected)
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- 9.1.1 describe the structure of the human gas exchange system, limited to: • lungs • trachea • bronchi • bronchioles • alveoli • capillary network
- 9.1.2 describe the distribution in the gas exchange system of cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries
- 9.1.3 recognise cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries in microscope slides, photomicrographs and electron micrographs
- 9.1.4 recognise trachea, bronchi, bronchioles and alveoli in microscope slides, photomicrographs and electron micrographs and make plan diagrams of transverse sections of the walls of the trachea and bronchus
- 9.1.5 describe the functions of ciliated epithelial cells, goblet cells and mucous glands in maintaining the health of the gas exchange system
- 9.1.6 describe the functions in the gas exchange system of cartilage, smooth muscle, elastic fibres and squamous epithelium
- 9.1.7 describe gas exchange between air in the alveoli and blood in the capillaries
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- 10.1.1 state that infectious diseases are caused by pathogens and are transmissible
- 10.1.2 malaria – caused by the protoctists Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax
- 10.1.3 tuberculosis (TB) – caused by the bacteria Mycobacterium tuberculosis and Mycobacterium bovis
- 10.1.4 HIV/AIDS – caused by the human immunodeficiency virus (HIV)
- 10.1.5 explain how cholera, malaria, TB and HIV are transmitted
- 10.1.6 discuss the biological, social and economic factors that need to be considered in the prevention and control of cholera, malaria, TB and HIV (details of the life cycle of the malarial parasite are not expected)
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- 10.2.1 outline how penicillin acts on bacteria and why antibiotics do not affect viruses
- 10.2.2 Antibiotic Resistance – Definition, Mechanism, Example.
- 10.2.3 Penicillin Production
- 10.2.4 Effect of Antibiotics on the Cell Wall
- 10.2.5 Difference Between Antiseptic and Antibiotic
- 10.2.6 Antibiotics definition, Characteristics, Classification, Administration
- 10.2.7 Mode of action of antibiotics and classification
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- 11.1.1 describe the mode of action of phagocytes (macrophages and neutrophils)
- 11.1.2 explain what is meant by an antigen and state the difference between self antigens and non-self antigens
- 11.1.3 describe the sequence of events that occurs during a primary immune response with reference to the roles of: • macrophages • B-lymphocytes, including plasma cells • T-lymphocytes, limited to T-helper cells and T-killer cells
- 11.1.4 explain the role of memory cells in the secondary immune response and in long-term immunity
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- 11.2.1 relate the molecular structure of antibodies to their functions
- 11.2.2 outline the hybridoma method for the production of monoclonal antibodies
- 11.2.3 outline the principles of using monoclonal antibodies in the diagnosis of disease and in the treatment of disease
- 11.2.4 describe the differences between active immunity and passive immunity
- 11.2.5 describe the differences between natural immunity and artificial immunity
- 11.2.6 explain how vaccination programmes can help to control the spread of infectious diseases
- 11.2.7 Monoclonal Antibodies – Definition, Types, Production, Side Effect, Applications
- 11.2.8 explain that vaccines contain antigens that stimulate immune responses to provide long-term immunity
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Practice
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