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OCR A-Level Biology H420

Cell Structure

Topic overview Microscopy, slide preparation and staining Biological drawings, magnification and resolution Eukaryotic cell ultrastructure The secretory pathway and the cytoskeleton Prokaryotic and eukaryotic cells compared

Biological Molecules

Topic overview The properties of water Monomers, polymers and the elements of life Monosaccharides and disaccharides Polysaccharides and their functions Lipids Amino acids and protein structure Globular and fibrous proteins Inorganic ions The biochemical tests Colorimetry and chromatography

Nucleotides and Nucleic Acids

Topic overview Nucleotide structure and the bases Polynucleotides, ADP and ATP The structure of DNA Semi-conservative DNA replication The genetic code, transcription and translation

Enzymes

Topic overview Enzyme action: lock and key and induced fit Factors affecting enzyme activity Cofactors, coenzymes and enzyme inhibition

Biological Membranes

Topic overview Membrane structure and the fluid mosaic model Factors affecting membrane permeability Diffusion, active transport, endocytosis and exocytosis Osmosis and water potential

Cell Division, Cell Diversity and Cellular Organisation

Topic overview The cell cycle Mitosis and observing it in root tips Meiosis Specialised cells Tissues, organs and organ systems Stem cells and differentiation

Exchange Surfaces

Topic overview Surface area to volume and the features of an exchange surface The mammalian gas exchange system Ventilation and lung volumes Gas exchange in fish and insects Dissecting and examining gas exchange tissue

Transport in Animals

Topic overview Why animals need transport systems Arteries, veins and capillaries Tissue fluid and lymph The structure of the mammalian heart The cardiac cycle and control of the heartbeat The electrocardiogram Transporting oxygen and carbon dioxide Oxygen dissociation curves and the Bohr effect

Transport in Plants

Topic overview Xylem, phloem and vascular tissue Transpiration and the potometer Water uptake and movement up the xylem Xerophytes and hydrophytes Translocation

Communicable Diseases, Disease Prevention and the Immune System

Topic overview Pathogens and how disease is transmitted Plant defences and non-specific animal defences Phagocytes and phagocytosis The specific immune response Antibodies Types of immunity Vaccination Medicines and antibiotic resistance

Biodiversity

Topic overview The three levels of biodiversity Sampling methods and equipment Simpson's Index of Diversity Measuring genetic biodiversity Threats to biodiversity and reasons to maintain it Conservation: in situ and ex situ

Classification and Evolution

Topic overview The taxonomic hierarchy and binomial naming The five kingdoms and the three domains Phylogeny and the evidence for evolution Variation and adaptation Natural selection and resistance

Communication and Homeostasis

Topic overview Cell signalling and communication systems Homeostasis, negative and positive feedback Thermoregulation in endotherms and ectotherms

Excretion as an Example of Homeostatic Control

Topic overview Excretion and nitrogenous waste The liver: structure and function The structure of the kidney The nephron Ultrafiltration Selective reabsorption and the loop of Henle Osmoregulation and ADH Kidney failure, dialysis and transplant Urine testing and monoclonal antibodies

Neuronal Communication

Topic overview Sensory receptors and the Pacinian corpuscle Types of neurone and myelination Resting potential and the action potential Transmission across a cholinergic synapse Summation and inhibitory synapses

Hormonal Communication

Topic overview Hormones and the adrenal glands The pancreas and the islets of Langerhans Controlling blood glucose Diabetes and its treatment

Plant and Animal Responses

Topic overview Tropisms and plant responses to stress and herbivory Plant hormones and their commercial uses The nervous system and the brain Reflex actions and the knee jerk reflex Fight or flight and the control of heart rate The structure of skeletal muscle The neuromuscular junction and the sliding filament model

Photosynthesis

Topic overview Photosynthesis and chloroplast structure Photosynthetic pigments and chromatography The light-dependent stage The Calvin cycle Limiting factors

Respiration

Topic overview Respiration, ATP and the mitochondrion Glycolysis The link reaction and the Krebs cycle Oxidative phosphorylation and chemiosmosis Anaerobic respiration Respiratory substrates and the respiratory quotient

Cellular Control

Topic overview Gene mutations and their effects The lac operon Transcription factors and post-transcriptional control Homeobox and Hox genes Mitosis and apoptosis Oncogenes, tumour suppressor genes and cancer

Patterns of Inheritance

Topic overview Genetic and environmental variation Monogenic and dihybrid inheritance, sex linkage and epistasis The chi-squared test Selection, genetic drift and the founder effect The Hardy-Weinberg principle Speciation and isolating mechanisms Artificial selection

Manipulating Genomes

Topic overview DNA sequencing and bioinformatics DNA profiling, PCR and gel electrophoresis Genetic engineering: restriction enzymes and vectors Genetic modification, its ethics, and gene therapy

Cloning and Biotechnology

Topic overview Natural plant cloning and taking cuttings Micropropagation Advantages and disadvantages of plant cloning Animal cloning: embryo twinning and nuclear transfer Advantages and disadvantages of animal cloning Microorganisms in food production Aseptic technique Fermentation and its conditions The microbial growth curve Immobilised enzymes

Ecosystems

Topic overview Ecosystems, biotic and abiotic factors Biomass transfer between trophic levels The nitrogen and carbon cycles Succession, distribution and abundance

Populations and Sustainability

Topic overview Population size and limiting factors Predator-prey cycles and competition Conservation and preservation Sustainable timber production and fishing Human impacts and how they are controlled

Practical Skills and Mathematical Requirements

Topic overview Planning investigations and choosing apparatus Recording and presenting data Gradients, intercepts and logarithmic scales Averages, spread and statistical tests Evaluating experiments and uncertainty Estimates, symbols and biological calculations

Plant and Animal Responses

7 subtopics
13 things to know
Components 01 and 03

What Plant and Animal Responses covers

Plant and animal responses is the fifth section of Module 5. It covers tropisms and the hormones behind them and their commercial uses, the organisation of the nervous system, the reflex arc, fight or flight and the control of heart rate, and how a muscle contracts.

Where it is assessed

Components 01 and 03

Module 5 is examined on Biological Processes, then the unified paper.

Check the OCR specification ↗

The 7 subtopics

Each one has its own page.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What do ethene, gibberellins and auxin do in leaf abscission, seed germination and apical dominance?

Process

Outline a reflex arc.

Process

Explain the sliding filament mechanism.

Process

What are auxins and what processes are they involved in?

Process

Explain the mechanism by which gibberellins promote seed germination.

Key term

Define apical dominance.

Key term

Define a reflex action.

Key term

What is the fight or flight response?

Key term

What is the role of calcium ions in initiating muscle contraction?

Key term

What are alkaloids and what is their function in plants?

Key term

What are the functions of the cerebrum?

Key term

What is the role of ATP in the detachment and re-cocking of myosin heads?

Key term

Describe the structure of a sarcomere.

Take Plant and Animal Responses further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

Tropism vs Nastic response
Tropism: a directional growth response to a stimulus. Nastic response: a non-directional response whose direction is independent of the stimulus.
Auxin vs Gibberellin
Auxin: the plant growth substance that promotes cell elongation in shoots. Gibberellin: the plant growth substance that stimulates amylase production to break down starch reserves in germinating seeds.
Sympathetic nervous system vs Parasympathetic nervous system
Sympathetic nervous system: the division that prepares the body for activity and raises heart rate. Parasympathetic nervous system: the division that returns the body to rest and lowers heart rate.

Questions from this topic

Each one with the model answer underneath.

1
What is a tropism?
Model answer
A directional growth response of a plant to an external stimulus, where the direction of growth is determined by the direction of the stimulus.
2
Define phototropism.
Model answer
The directional growth response of a plant towards or away from a light source.
3
What is geotropism (gravitropism)?
Model answer
The directional growth response of a plant towards or away from gravity.
4
Distinguish between positive and negative tropism.
Model answer
Positive tropism is growth towards a stimulus; negative tropism is growth away from a stimulus.
5
How do plants respond to abiotic stress?
Model answer
Through physiological and morphological changes that help them survive unfavourable environmental conditions.
6
What is herbivory, and why have plants evolved responses to it?
Model answer
Herbivory is the consumption of plant material by animals. Plants have evolved responses to deter or limit damage from herbivores.

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Cell Structure

Biological Molecules

Nucleotides and Nucleic Acids

Enzymes

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Centrioles consist of .

microtubuleschromosomesribosomes

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AA phospholipid contains one glycerol molecule.

BTwo fatty acids bond to the glycerol molecule.

COne phosphate group replaces the third fatty acid.

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Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Habitat means the physical place where an organism lives.

TrueFalse

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Spot the fault in a statement. The traps are the mistakes students actually make.

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Plant and Animal Responses revision questions

What does Plant and Animal Responses cover in OCR A-Level Biology?: 7 subtopics: tropisms and plant responses to stress and herbivory, plant hormones and their commercial uses, the nervous system and the brain, reflex actions and the knee jerk reflex, fight or flight and the control of heart rate, the structure of skeletal muscle and the neuromuscular junction and the sliding filament model. Each one has its own page with questions and model answers.
How is Plant and Animal Responses organised?: By the OCR H420 specification, subtopic by subtopic, so it matches the order you are taught it in.

Every question in Plant and Animal Responses, on a schedule.

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