What is meant by describing the human body as a host?

The human body provides the habitat, warmth, water and nutrients in which other organisms live, and those organisms depend on it for their survival.

Why can a long course of antibiotics upset the digestive system?

The antibiotic kills much of the normal gut flora as well as the pathogen, removing the competition that normally holds resistant bacteria and yeasts in check, so those species overgrow.

What is an opportunistic pathogen?

An opportunistic pathogen is an organism that is harmless in a healthy person but causes disease when the host's defences are weakened or when it reaches a tissue it does not normally occupy.

Eduqas A-Level Biology A400QS

Biological Molecules

Topic overview Inorganic ions and the properties of water Monosaccharides and disaccharides Polysaccharides, storage and structure Lipids, triglycerides and phospholipids Amino acids and protein structure Condensation, hydrolysis and the food tests

Cell Structure and Organisation

Topic overview The nucleus and the endomembrane system Mitochondria, chloroplasts and other organelles Prokaryotic cells and viruses Cell theory, microscopy and measuring cells Comparing cells and the levels of organisation

Cell Membranes and Transport

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Enzymes

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Nucleic Acids and Their Functions

Topic overview Nucleotides and the structure of ATP ATP as the energy currency of the cell The structure of DNA Comparing DNA and RNA Semi-conservative replication The genetic code Transcription Translation and the fate of the polypeptide Extracting DNA from living material

Importance of ATP

Topic overview ATP synthetase and the synthesis of ATP Chemiosmosis and the electrochemical gradient Proton pumps and the electron transport chain Membranes of mitochondria and chloroplasts compared Investigating dehydrogenase activity

Photosynthesis

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Respiration

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Microbiology

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Human Impact on the Environment

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Mitosis and Meiosis

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Sexual Reproduction in Humans

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Sexual Reproduction in Plants

Topic overview Flower structure and the contrast between wind and insect pollination The development of pollen grains and ovules Pollination and double fertilisation The formation and structure of seed and fruit Germination of Vicia faba and the action of gibberellin

Inheritance

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Variation and Evolution

Topic overview Genetic and environmental sources of variation Investigating continuous variation and the t test Competition and selective agencies Gene pools, genetic drift and selection The Hardy-Weinberg principle Isolation, speciation and Darwin's theory of evolution

Application of Reproduction and Genetics

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Adaptations for Gas Exchange

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Adaptations for Transport

Topic overview Vascular systems compared across animal groups The mammalian heart and blood vessels The cardiac cycle and its control Blood, haemoglobin and dissociation curves The Bohr effect, chloride shift and tissue fluid The root and the uptake of water The endodermis and the entry to the xylem Xylem, transpiration and cohesion-tension The potometer and xerophytes and hydrophytes Phloem and translocation

Adaptations for Nutrition

Topic overview Modes of nutrition Saprotrophic nutrition Holozoic nutrition and the unicellular gut From a sac-like gut to a tube gut The human gut and the effect of diet Herbivores, carnivores and parasites

Homeostasis and the Kidney

Topic overview Homeostasis and feedback The structure of the kidney and the nephron Ultrafiltration and selective reabsorption Water regulation and antidiuretic hormone Excretory products, adaptation and kidney failure

The Nervous System

Topic overview The components of a nervous response The spinal cord and spinal nerves The reflex arc and nerve nets The structure of a motor neurone The nerve impulse Oscilloscope traces and conduction speed The synapse and synaptic transmission Chemicals affecting transmission

Immunology and Disease: Disease and Its TransmissionImmunology

Topic overview The language of infection and disease The human body as a host Cholera and tuberculosis Smallpox, influenza and viral pathogenicity Malaria and its transmission

Immunology and Disease: AntibioticsImmunology

Topic overview Bacteriostatic and bactericidal antibiotics Broad and narrow spectrum antibiotics Penicillin and the bacterial cell wall Tetracycline and the Gram negative barrier The spread of antibiotic resistance

Immunology and Disease: The Immune ResponseImmunology

Topic overview Natural barriers to infection Inflammation, clotting and phagocytosis Antigens, B lymphocytes and the humoral response Cell-mediated immunity and T lymphocytes Active and passive immunity Vaccination programmes and their ethics

Human Musculoskeletal Anatomy: Skeletal TissuesMusculoskeletal

Topic overview Cartilage and its three types The composition and functions of compact bone Bone remodelling and the Haversian system Rickets, osteomalacia, osteoporosis and brittle bone disease The structure of skeletal muscle The sliding filament theory Fast and slow twitch fibres, and energy for contraction

Human Musculoskeletal Anatomy: Structure and Function of the SkeletonMusculoskeletal

Topic overview The axial and appendicular skeleton The girdles and the bones of the limbs The vertebral column and its vertebrae Fractures and postural deformities The functions of the skeleton

Human Musculoskeletal Anatomy: JointsMusculoskeletal

Topic overview Types of joint in the human body The structure of a synovial joint Osteoarthritis and rheumatoid arthritis Joints as levers Antagonistic muscle action in the forelimb

Neurobiology and Behaviour: The BrainNeurobiology

Topic overview The structure of the human brain The functions of the cerebrum, cerebellum and medulla oblongata The hypothalamus and the control of the endocrine system The sympathetic and parasympathetic nervous systems Sensory and motor areas, the homunculus and language

Neurobiology and Behaviour: NeuroscienceNeurobiology

Topic overview Non-invasive study of the brain: CT and MRI Functional imaging: fMRI, PET and EEG Brain development and critical periods Neuroplasticity Gene expression, brain development and mental illness

Neurobiology and Behaviour: BehaviourNeurobiology

Topic overview Innate behaviour: escape reflexes, kineses and taxes Habituation and imprinting Classical and operant conditioning Primate societies and the costs and benefits of group living Insect castes, dominance hierarchies, territory and courtship

Immunology and Disease: Disease and Its Transmission

The human body as a host

3 things to know
Component 3

Overview

Describing the human body as a host, opportunistic pathogen and faecal–oral route of transmission.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Name three regions of the human body that normally carry a resident population of microorganisms.

Key term

Distinguish a commensal from a parasite.

Key term

How does the normal bacterial flora of the gut benefit its human host?

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by describing the human body as a host?
Model answer
The human body provides the habitat, warmth, water and nutrients in which other organisms live, and those organisms depend on it for their survival.
2
Name three regions of the human body that normally carry a resident population of microorganisms.
Model answer
The skin, the large intestine and the mouth all carry a normal resident population of microorganisms.
3
Distinguish a commensal from a parasite.
Model answer
A commensal lives on or in the host and gains from it while doing the host no measurable harm, whereas a parasite gains from the host at the host's expense.
4
How does the normal bacterial flora of the gut benefit its human host?
Model answer
The gut flora synthesises vitamin K and some B vitamins, helps digest material the gut cannot break down, and occupies the sites and nutrients that incoming pathogens would otherwise use.
5
Why can a long course of antibiotics upset the digestive system?
Model answer
The antibiotic kills much of the normal gut flora as well as the pathogen, removing the competition that normally holds resistant bacteria and yeasts in check, so those species overgrow.
6
What is an opportunistic pathogen?
Model answer
An opportunistic pathogen is an organism that is harmless in a healthy person but causes disease when the host's defences are weakened or when it reaches a tissue it does not normally occupy.

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