Cambridge AS Level Biology (9700) Comprehensive Review

Flashcards covering key syllabus concepts for Cambridge International AS Level Biology (9700), including Cell Structure, Biological Molecules, Enzymes, Cell Membranes, Mitosis, Nucleic Acids, Plant Transport, Mammalian Transport, Gas Exchange, Infectious Diseases, and Immunity.

What is the definition of resolution in microscopy?

The ability to distinguish between two points or objects that are very close together. For a light microscope, the maximum resolution is $200\,nm$ ($0.2\,\mu m$).

What is the formula used to calculate the magnification of a microscopic image?

$\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}$ (or $M = \frac{I}{A}$), where image size and actual size are converted to the same units before calculation.

What are the key structural features always present in a generalized prokaryotic cell?

A cell wall containing murein (peptidoglycan), a cell surface membrane, cytoplasm, circular DNA (not enclosed in a nuclear envelope), and $70\text{S}$ ribosomes.

How is the biochemical test for non-reducing sugars carried out?

Boil the sample with dilute hydrochloric acid to hydrolyse glycosidic bonds. Neutralise with sodium hydrogencarbonate, then add Benedict's reagent and heat in a water bath to observe a brick-red precipitate.

How do the molecular structures of amylose and amylopectin in starch differ?

Amylose is an unbranched polymer of $\alpha$-glucose linked by $\alpha\text{-}1,4$ glycosidic bonds that coiling into a helix, whereas amylopectin is a branched polymer containing both $\alpha\text{-}1,4$ and $\alpha\text{-}1,6$ glycosidic bonds.

Describe the structural organization of a collagen molecule.

It consists of three helical polypeptide chains (with glycine as every third amino acid) wound around each other to form a triple helix, stabilized by hydrogen bonds and covalent cross-links.

How do competitive and non-competitive inhibitors alter the $V_{\max}$ and $K_m$ of an enzyme-catalysed reaction?

Competitive inhibitors increase $K_m$ (reducing enzyme affinity) without changing $V_{\max}$; non-competitive inhibitors decrease $V_{\max}$ without changing $K_m$.

How are enzymes immobilized using sodium alginate and calcium chloride?

The enzyme is mixed with sodium alginate solution and dropped into calcium chloride solution, forming insoluble jelly beads that trap and immobilize the enzyme.

Why is the structure of cell surface membranes described as a 'fluid mosaic'?

It is 'fluid' because individual phospholipid molecules and proteins can move laterally within their monolayer, and 'mosaic' because the embedded proteins are scattered throughout the bilayer.

How does the sodium-potassium ($\text{Na}^+\text{-}\text{K}^+$) pump operate across the cell surface membrane?

It uses ATP hydrolysis to actively transport $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell against their concentration gradients.

What are the primary roles of mitosis in multicellular organisms?

Growth of the organism, repair of damaged tissues, replacement of dead cells, and asexual reproduction, producing genetically identical daughter cells.

What is the primary function of telomeres on eukaryotic chromosomes?

They prevent the loss of vital genes near the ends of chromosomes during DNA replication and stop chromosome ends from fusing together.

What are the complementary base pairing rules and hydrogen bonding numbers in a DNA double helix?

Adenine pairs with Thymine via $2$ hydrogen bonds, and Cytosine pairs with Guanine via $3$ hydrogen bonds.

What are the functions of DNA polymerase and DNA ligase during DNA replication?

DNA polymerase adds complementary free nucleotides to the growing strand in a $5'$ to $3'$ direction; DNA ligase joins Okazaki fragments together on the lagging strand.

List four structural adaptations of xylem vessel elements for transporting water.

Lignified cell walls prevent collapse under tension; dead hollow lumen without cytoplasm allows continuous mass flow; end walls are absent forming continuous tubes; pits allow lateral movement of water.

How do companion cells load sucrose into phloem sieve tube elements?

Proton pumps use ATP to pump $\text{H}^+$ ions out of companion cells into the cell wall. $\text{H}^+$ ions diffuse back through $\text{H}^+\text{/sucrose}$ cotransporter proteins, carrying sucrose into companion cells, which then passes into sieve elements via plasmodesmata.

How is marram grass (Ammophila arenaria) structurally adapted as a xerophyte?

Inrolled leaves trap humid air inside; stomata are sunken in pits; a thick waxy cuticle containing cutin reduces cuticular transpiration; trichomes (leaf hairs) trap a moist boundary layer.

How do the structural features of muscular/elastic arteries differ from those of veins?

Arteries have thicker muscular and elastic walls, narrower lumens, operate under high pressure ($10\text{--}16\,kPa$), and lack valves (except at exits of the heart); veins have thinner walls, wider lumens, low pressure ($1\,kPa$), and semilunar valves.

Describe the electrical conduction pathway during a single cardiac cycle.

The sinoatrial node (SAN) generates a wave of excitation causing atrial systole -> wave reaches the atrioventricular node (AVN) which delays it by $0.1\,s$ -> excitation travels down the septum via Purkyne tissue to the apex -> spreads upwards through ventricle walls causing ventricular systole.

What is the Bohr shift and how does it benefit active respiring tissues?

High $\text{pCO}_2$ in active tissues forms carbonic acid ($\text{H}_2\text{CO}_3$) via carbonic anhydrase, which dissociates into $\text{H}^+$ and $\text{HCO}_3^-$. $\text{H}^+$ binds haemoglobin to form haemoglobinic acid ($\text{HHb}$), lowering its affinity for oxygen and causing oxygen release into respiring tissues.

What is the distribution of cartilage, ciliated epithelium, goblet cells, and smooth muscle in human gas exchange airways?

Trachea & bronchi contain cartilage, ciliated epithelium, goblet cells, and smooth muscle; terminal bronchioles contain smooth muscle and cilia but no cartilage or goblet cells; alveoli contain squamous epithelium and elastic fibres only.

What are the causative pathogens and transmission methods for Cholera, Malaria, Tuberculosis, and HIV/AIDS?

Cholera: Vibrio cholerae (bacterium, water/food-borne); Malaria: Plasmodium species (protoctist, female Anopheles mosquito vector); Tuberculosis: Mycobacterium tuberculosis/bovis (bacterium, airborne droplets); HIV/AIDS: Human Immunodeficiency Virus (virus, body fluids/sexual intercourse/blood).

How does penicillin act on bacteria, and why does it have no effect on viruses?

Penicillin inhibits transpeptidase, preventing peptidoglycan cross-linking in bacterial cell walls during growth, causing cell lysis; viruses lack cell walls, peptidoglycan, and metabolic machinery.

Outline the main steps of phagocytosis carried out by neutrophils.

1. Chemotaxis/attraction to pathogen; 2. Binding to non-self antigens/antibody markers; 3. Endocytosis/engulfment into a phagocytic vacuole; 4. Fusion of lysosomes with the vacuole; 5. Digestion of the pathogen by hydrolytic enzymes.

How are monoclonal antibodies produced using the hybridoma method?

A mouse is injected with a specific antigen to produce B plasma cells in its spleen; these plasma cells are fused with cancerous myeloma cells to form hybridoma cells, which are screened to isolate clones producing the target antibody.