QCAA Year 11 Biology Units 1 & 2 Revision Guide

A comprehensive set of Q&A flashcards covering Unit 1 (Cells and Multicellular Organisms) and Unit 2 (Homeostasis and Infectious Disease) based on the QCAA Year 11 Biology syllabus.

How do prokaryotic and eukaryotic cells differ in terms of their DNA storage?

Prokaryotic DNA is located in a nucleoid and often contains plasmids, while eukaryotic DNA is enclosed within a membrane-bound nucleus and organized into multiple linear chromosomes.

What are four similarities shared by both prokaryotic and eukaryotic cells?

Both cell types possess a cell membrane, cytoplasm, DNA, and ribosomes.

What is the biological role of the mitochondria?

They are the site of aerobic respiration and the production of $ATP$.

What is the primary difference in function between the Rough Endoplasmic Reticulum (RER) and the Smooth Endoplasmic Reticulum (SER)?

The RER modifies and transports proteins made for secretion or membranes via attached ribosomes, whereas the SER is responsible for lipid synthesis, detoxification, and metabolic functions.

How does the large central vacuole contribute to plant cell structure?

It stores water and dissolved substances while maintaining turgor pressure to support the cell.

Define mitosis and state its biological purposes.

Mitosis is nuclear division producing two genetically identical daughter cells with the same chromosome number as the parent; it is used for growth, repair, replacement, and asexual reproduction.

Distinguish between totipotent and pluripotent stem cells.

Totipotent cells can form every cell type including extra-embryonic tissues and a complete organism, while pluripotent cells can form almost any body cell type but cannot form a complete organism alone.

What is the hierarchical organization of multicellular organisms?

The hierarchy is Cell $\rightarrow$ tissue $\rightarrow$ organ $\rightarrow$ organ system $\rightarrow$ organism.

Explain why intestinal epithelial cells have microvilli.

Microvilli provide a larger surface area to volume ratio ($SA:V$), which allows for faster nutrient absorption.

Describe the components and function of the fluid mosaic model of the cell membrane.

It consists of a phospholipid bilayer (hydrophilic heads and hydrophobic tails) with embedded proteins, cholesterol for stability/fluidity, and glycoproteins for recognition, forming a selectively permeable barrier.

Define osmosis.

The net movement of water across a selectively permeable membrane from a region of higher water concentration (lower solute) to a region of lower water concentration (higher solute).

How does active transport differ from passive transport?

Active transport requires energy (usually $ATP$) to move substances against a concentration gradient, whereas passive transport requires no energy and moves substances down a gradient.

Why is a high $SA:V$ ratio critical for cell efficiency?

A high ratio provides more membrane area for exchange relative to volume and shorter diffusion distances, allowing for faster exchange of nutrients, gases, and wastes.

What are the primary functions of carbohydrates in organisms?

They serve as an immediate energy source (glucose), for energy storage (glycogen in animals, starch in plants), and provide structural support (cellulose in plant cell walls).

How do digestive enzymes like amylase, protease, and lipase simplify biomolecules?

Amylase breaks starch into smaller sugars; proteases break proteins into peptides and amino acids; lipases break lipids into fatty acids and glycerol.

Identify four features that make exchange surfaces efficient.

Efficient surfaces have a large surface area, a thin barrier for short diffusion distance, a moist surface for dissolution, and a good blood supply to maintain concentration gradients.

What are the advantages of a closed circulatory system?

It maintains blood at relatively high pressure, ensures rapid bulk transport, allows blood flow to be directed to specific tissues, and maintains steep concentration gradients at exchange surfaces.

What is the function of the Glomerulus in the nephron?

It is a capillary knot where high hydrostatic pressure drives the filtration of water and small solutes into Bowman's capsule.

Explain the role of the Loop of Henle.

It establishes an osmotic gradient in the medulla which is essential for concentrating urine.

How do enzymes act as biological catalysts?

Enzymes lower the activation energy required for a reaction, thereby increasing the reaction rate without being consumed.

Compare the lock-and-key model with the induced-fit model of enzyme action.

The lock-and-key model suggests a rigid, perfectly complementary active site, while the induced-fit model suggests the active site is flexible and changes shape slightly upon substrate binding to improve catalysis.

How does temperature affect enzyme activity beyond the optimum level?

High temperatures disrupt the bonds maintaining the enzyme's shape, leading to the denaturation of the active site and a sharp fall in the reaction rate.

Distinguish between catabolism and anabolism.

Catabolism involves breaking complex molecules into simpler ones to release energy, while anabolism uses energy to build complex molecules from simpler ones.

State the overall equation for aerobic respiration.

$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$$

What occurs during the electron transport chain stage of respiration?

Electrons from carriers like $NADH$ and $FADH_2$ create an $H^+$ gradient that drives $ATP$ production through $ATP$ synthase, with $O_2$ acting as the final electron acceptor to form water.

Predict the direction of gas exchange between the blood and active muscle.

$O_2$ diffuses from the blood into the muscle (used in respiration), and $CO_2$ diffuses from the muscle into the blood (produced by respiration).

State the overall equation for photosynthesis.

$$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$$

How do Xylem and Phloem differ in content and direction of transport?

Xylem transports water and minerals mainly upward from roots; Phloem translocates organic solutes (sugars) from sources to sinks in multiple directions.

Explain how guard cells control stomatal opening.

When guard cells gain water and become turgid, the stomatal pore opens; when they lose water and become flaccid, the pore closes.

List four factors that affect the rate of transpiration.

Light intensity, temperature, wind speed, and relative humidity.

Identify the eight steps of the negative-feedback model.

Stimulus $\rightarrow$ Receptor $\rightarrow$ Communication pathway $\rightarrow$ Control centre $\rightarrow$ Communication pathway $\rightarrow$ Effector $\rightarrow$ Response $\rightarrow$ Variable returns toward set point.

What is the function of sensory, inter, and motor neurons?

Sensory neurons carry signals from receptors to the CNS; interneurons connect signals within the CNS; motor neurons carry orders from the CNS to effectors (muscles/glands).

Describe the ion movement maintained by the sodium-potassium pump.

The pump uses $ATP$ to move $3\text{ }Na^+$ out of the neuron and $2\text{ }K^+$ in to maintain the resting membrane potential.

How does an action potential traverse a myelinated axon?

Through saltatory conduction, where the depolarization jumps between gaps in the myelin called Nodes of Ranvier, increasing conduction speed.

Define a hormone.

A chemical messenger released by endocrine glands into the blood that affects distant target cells containing specific matching receptors.

How do endotherms regulate body temperature through physiological mechanisms?

They use vasodilation to increase heat loss, vasoconstriction to reduce heat loss, evaporative cooling (sweating/panting), and thermogenesis (shivering/metabolic changes).

Explain the response to high blood osmolarity (dehydration).

Osmoreceptors trigger the release of $ADH$ from the posterior pituitary, which increases aquaporins in the kidney collecting ducts, leading to more water reabsorption and concentrated urine.

What role does Abscisic acid (ABA) play in plant water balance?

It is a hormone that increases during water stress to promote stomatal closure, thereby conserving water.

Identify the unique characteristics of prions and viruses.

Prions are infectious misfolded proteins without a genome; viruses are acellular particles with a DNA or RNA genome enclosed in a protein capsid that require a host to replicate.

What are major histocompatibility complex (MHC) proteins?

Surface molecules on body cells that help the immune system identify the cell as 'self'.

Describe the events of the inflammatory response.

Signalling molecules cause vasodilation (redness/heat) and increased capillary permeability (swelling); chemotaxis attracts leukocytes like neutrophils and macrophages to phagocytose pathogens.

Contrast the humoral and cell-mediated immune responses.

Humoral immunity involves B lymphocytes producing antibodies to target antigens in body fluids; cell-mediated immunity involves T lymphocytes (such as Cytotoxic T cells) destroying infected or abnormal cells.

Differentiate between active and passive immunity.

Active immunity results from an individual's own immune response and creates memory cells for long-term protection; passive immunity involves receiving pre-made antibodies and provides immediate but temporary protection without memory.

Why is the secondary immune response faster and stronger than the primary response?

Because of the presence of memory B and T cells that rapidly activate and expand upon re-exposure to the same antigen.

What is herd immunity?

Indirect protection from an infectious disease that occurs when a large enough proportion of a population is immune, making sustained transmission unlikely.

Explain the difference between isolation and quarantine.

Isolation separates people known to be infected, while quarantine restricts the movement of people who may have been exposed during the incubation period.