Biological ScienceLife ProcessesYear 8 Science

Hormones, the menstrual cycle, flowers and fungi

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What this lesson covers

What a hormone is and how it reaches its target
How hormones control ovulation and the uterus lining
Hormones and sperm production
The stages of reproduction in flowering plants
How most fungi reproduce with spores
Organising information to compare processes

Key idea

Hormones: messages in the blood

A hormone is a chemical messenger. It is made in one part of the body, released into the blood, and carried all round the body.
It only affects certain target cells or tissues, which have the right receptors to respond to it, and it changes what those cells do.
For example, insulin from the pancreas tells liver and muscle cells to take up sugar, and adrenaline gets the body ready for action when you are scared.
Reproduction is controlled by hormones too, mainly from the pituitary gland at the base of the brain and from the ovaries or testes.

Key idea

The menstrual cycle

From puberty, a female's body goes through a repeating cycle, often about 28 days long, though it varies from person to person and month to month.
Hormones make an egg mature in an ovary and the lining of the uterus grow thick and full of blood vessels, ready to receive a fertilised egg.
About halfway through the cycle, an egg is released from the ovary. This is ovulation.
If the egg is not fertilised, hormone levels fall and the thick lining breaks down and leaves the body through the vagina over a few days. This bleeding is menstruation, or a period.
Then the cycle starts again. If the egg is fertilised, hormones keep the lining in place and periods stop during pregnancy.

A circle for a 28-day cycle: days 1 to 5 the lining is shed in a period; days 6 to 13 the lining thickens; about day 14 an egg is released; days 15 to 28 the lining is kept ready

Key idea

Hormones and sperm production

From puberty, the testes make sperm all the time, millions every day, rather than in a monthly cycle.
This is controlled by hormones from the pituitary gland, which signal the testes.
The testes make the hormone testosterone, which keeps sperm production going and also causes changes at puberty, such as a deeper voice and more body hair.

Worked example

Organising: female and male gametes

Organise the facts about gamete production into a table, then state one similarity and one difference.

	Female	Male
Gamete	Egg (ovum)	Sperm
Where made	Ovaries	Testes
How often released	About once a month	Made continuously
Controlled by	Hormones from the pituitary and ovaries	Hormones from the pituitary and testes

Similarity: both are controlled by hormones, including ones from the pituitarythe last row matches
Difference: eggs are released in a monthly cycle, sperm are made all the timethe third row differs
One similarity and one difference, each taken from a row of the table

Key idea

Try it: egg or sperm?

Key idea

How flowering plants reproduce

Pollination: pollen, carrying the male gamete, moves from an anther to the stigma of a flower, carried by wind, insects or birds. Tūī and korimako (bellbirds) pollinate kōwhai and harakeke as they feed on nectar.
Fertilisation: a tube grows from the pollen grain down to the ovary, and the male gamete joins an egg cell inside an ovule.
Seed formation: the fertilised ovule becomes a seed holding a tiny plant and a food store, and the ovary around it often becomes a fruit.
Seed dispersal: seeds are spread away from the parent by wind, water or animals. Kererū swallow large berries such as those of taraire and tawa and drop the seeds far away.
Germination: with water, warmth and oxygen, the seed swells, a root grows down and a shoot grows up, starting a new plant.

A loop of five stages for a flowering plant: pollination, then fertilisation, then seed formation, then seed dispersal, then germination, leading to a new plant that flowers

Key idea

Try it: put the steps in order

Worked example

Why a forest needs kererū

Some native trees have berries so large that only the kererū can swallow them. Explain what could happen to these trees if kererū disappeared from a forest.

Kererū swallow the berries and drop the seeds elsewherethis is seed dispersal
Without kererū, the berries fall under the parent treeno other animal carries them
Seedlings there compete with the parent for light and watermost fail
Fewer new trees grow in new places, so these trees slowly become rarer

Key idea

Fungi reproduce with spores

Most fungi reproduce by making spores: tiny cells, far too small to see one by one, that can grow into a new fungus.
Moulds, such as the fuzz on old bread, make spores directly on short stalks that grow up from their threads. The dark dots you see are clusters of spores.
Mushrooms make spores on thin gills or in tiny tubes under the cap. A single mushroom can release millions.
Spores are so light that air currents carry them a long way. If one lands somewhere damp with food, it germinates and grows threads, starting a new fungus.

Common mistakes

A hormone works on every cell it reaches in the blood.
A hormone travels everywhere in the blood but only changes the target cells that can respond to it.
A period is when the egg is released.
The egg is released at ovulation, about halfway through the cycle; a period is the lining being shed when no fertilisation happened.
Pollination and fertilisation are the same thing.
Pollination moves pollen to the stigma; fertilisation happens later, when the male gamete joins the egg inside the ovule.
Mushrooms grow from seeds.
Fungi have no seeds; they grow from spores, which are single tiny cells.

Try it at home

Make a mushroom spore print

You need: a fresh flat (open) mushroom from the supermarket, a sheet of white paper, a sheet of dark paper, a bowl or glass to cover it

Gently pull the stalk off the mushroom so the gills underneath are showing.
Put the cap gills-down so it sits half on the white paper and half on the dark paper.
Cover it with the upturned bowl so no draught moves the air, and leave it overnight.
Lift the bowl and the cap off very carefully.
Look for a print of fine lines matching the gills: it is made of millions of spores that fell from the gills, too small to see one at a time.

Safety: Use only mushrooms bought from a shop and never pick wild ones, because some New Zealand wild mushrooms are deadly; wash your hands after handling it, and throw it away afterwards rather than eating it.

Your turn

Give the three parts of the definition of a hormone.

What happens to the lining of the uterus if an egg is not fertilised?

Which hormone made by the testes keeps sperm production going?

Put these in order: germination, pollination, seed dispersal, fertilisation, seed formation.

Why can a mould appear on bread in a closed bag, even though nobody put it there?

Show answer

1. A chemical messenger, carried in the blood, that changes how its target cells work. 2. It breaks down and leaves the body as menstruation, a period. 3. Testosterone. 4. Pollination, fertilisation, seed formation, seed dispersal, germination. 5. Mould spores are tiny and floating in the air everywhere, so some were already on the bread or in the bag and germinated.

Summary

Recap

A hormone is a chemical messenger carried in the blood that changes how its target cells work.
In the menstrual cycle, hormones control ovulation and the thickening of the uterus lining, which is shed as a period if no fertilisation happens.
Hormones from the pituitary and the testes keep sperm production going.
Flowering plants go through pollination and fertilisation, then form seeds, which are dispersed and germinate.
Most fungi reproduce by spores that drift in the air and germinate where it is damp and there is food.

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