A chemical messenger made by an endocrine gland that travels in the blood and affects target organs.

How are hormones carried from the gland that made them to the organ they affect?

They are released into the bloodstream and carried dissolved in the blood plasma.

Name four endocrine glands in the human body.

The pituitary gland, the thyroid gland, the pancreas and the adrenal glands.

Where are the adrenal glands found?

One sits just above each kidney.

OCR GCSE Biology A J247

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Protein synthesis and the triplet code Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition and trophic levels Pyramids of biomass and the efficiency of transfer

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations How genetic variants influence phenotype Asexual and sexual reproduction compared Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination, multiple genes and Mendel's work Variation within a population, and classification Natural selection and evolution Evidence for evolution, and the work of Darwin and Wallace

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, and evidence for environmental change Food security, agricultural and biotechnological solutions Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples Physical and chemical plant defences Detecting plant disease; white blood cells and platelets Non-specific defences and the immune system Monoclonal antibodies and their uses Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc The eye and its common defects The structure and function of the brain Investigating and treating the brain Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Plant hormones and their commercial uses Homeostasis, and the skin in temperature control Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes Osmotic changes in body fluids, and the kidneys The kidney tubule and the effect of ADH Responding to temperature and osmotic challenges

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Organism Level Systems

Hormonal coordination, thyroxine and adrenaline

3 things to know
Paper 3

Overview

What hormones and endocrine glands are and how hormones affect only their target organs, the main endocrine glands and sex hormones, how hormonal and nervous responses compare, thyroxine and how thyroid stimulating hormone and negative feedback control it, and how adrenaline prepares the body for action.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is a hormone?

Key term

What is an endocrine gland?

Key term

A hormone reaches every organ, so why does it affect only some of them?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a hormone?
Model answer
A chemical messenger made by an endocrine gland that travels in the blood and affects target organs.
2
How are hormones carried from the gland that made them to the organ they affect?
Model answer
They are released into the bloodstream and carried dissolved in the blood plasma.
3
What is an endocrine gland?
Model answer
A gland that releases its hormones directly into the blood rather than through a duct.
4
A hormone reaches every organ, so why does it affect only some of them?
Model answer
Only the target organs have cells carrying receptors that the hormone molecule fits, so only those cells respond.
5
Name four endocrine glands in the human body.
Model answer
The pituitary gland, the thyroid gland, the pancreas and the adrenal glands.
6
Where are the adrenal glands found?
Model answer
One sits just above each kidney.

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Cell Level Systems

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Genes, Inheritance and Selection

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Algae and .

phytoplanktonfungianimals

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AThe blood becomes too dilute.

BLess ADH is released.

CThe collecting ducts become less permeable.

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Egestion means passing out of undigested food as faeces.

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