Science notes, unit 2

Humans

Textbook Science Year 6 (DLP, Semakan 2017), pages 13–32

What this chapter covers

You can name the male and female reproductive organs and state what each one does (2.1.1)
You can describe the process from fertilisation to birth in the correct order (2.1.2)
You can explain why reproduction is important to humans (2.1.3)
You can name the two parts of the nervous system and what each is made of (2.2.1)
You can explain what the brain and the spinal cord do, and tell voluntary, involuntary and reflex actions apart (2.2.2)
You can explain what the peripheral nervous system does and give examples of damage to it (2.2.3, 2.2.4)
You can give ways to take care of the nervous system (2.2.5)

Your body can make new life and it can react in a split second. In this unit you will learn how humans reproduce and how the nervous system controls the body.

2.1Human reproduction

Reproduction is how humans make new individuals so that the human species survives. It needs a man and a woman. Their reproductive organs make up the reproductive system.

Male reproductive organs

The male reproductive organs are the testes and the penis.

Organ	Function
Testis (plural: testes)	Produces sperms.
Penis	Transfers sperms into the female reproductive organ.

Male reproductive organs: the testes and the penis, with a labelled enlarged view — The male reproductive organs.

Figure: Science Year 6 textbook, p.14.

Female reproductive organs

The female reproductive organs are the ovaries, Fallopian tubes, uterus and vagina.

Organ	Function
Ovary	Produces ova (eggs) every month. One is an ovum.
Fallopian tube	The place where a sperm and an ovum meet and fuse (fertilisation).
Uterus (womb)	The organ where the embryo develops and grows.
Vagina	A channel that receives sperms from the penis.

Female reproductive organs with the uterus, ovaries, Fallopian tubes and vagina labelled — The female reproductive organs.

Figure: Science Year 6 textbook, p.15.

Did you know? A boy's testes start making sperms at puberty. A girl's ovaries start releasing ova at puberty. If the ovary releases more than one ovum and both are fertilised, twins or more may be born.

The ovary makes the ovum, but fertilisation does not happen in the ovary. It happens in the Fallopian tube. The embryo grows in the uterus.

Which organ produces sperms and which produces ova?

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Testes produce sperms. Ovaries produce ova.

From fertilisation to birth

Fertilisation is the fusion of a sperm from the male parent with an ovum from the female parent.

The penis transfers sperms into the vagina.
Sperms swim towards the ovum using their tails. One sperm fuses with the ovum in the Fallopian tube. This is fertilisation.
The fertilised ovum is a zygote. It divides again and again to form many cells called an embryo.
The embryo moves to the uterus and develops into a foetus.
The foetus stays in the uterus for about nine months until its organs are completely developed.
The mother gives birth through the vagina. The foetus is now a baby.

Diagram of a sperm fusing with an ovum in the Fallopian tube, the zygote dividing, and the embryo reaching the uterus — Fertilisation to embryo, steps 1 to 3 in the textbook.

Figure: Science Year 6 textbook, p.16.

Stage	Name
Ovum + sperm fused	Zygote
Zygote divides into many cells	Embryo
Embryo grows in the uterus	Foetus
Born after about nine months	Baby

Umbilical cord. The foetus is joined to its mother by the umbilical cord. It brings nutrients and oxygen from the mother to the foetus and takes waste products away.

Put these in order: foetus, zygote, baby, embryo.

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Zygote, embryo, foetus, baby.

Why reproduction is important

It increases the number of humans (the population). A family with no new babies stays the same size and grows old.
It makes sure the human species survives. If nobody reproduced, humans would become extinct.

2.2The human nervous system

When a mosquito bites your hand you shake it off. When you bite a sour orange you taste the sourness at once. The system that controls and coordinates all this is the nervous system. It detects a stimulus and tells the body how to respond.

Nervous system: the brain, the spinal cord and a network of nerves through the body. Its basic unit is the nerve cell (neuron).

Two parts of the nervous system

Human body outlines showing the brain and spinal cord, and the network of nerves — Central nervous system (brain and spinal cord) and peripheral nervous system (neural network).

Figure: Science Year 6 textbook, p.21.

Part	Made of	Job
Central nervous system (CNS)	Brain and spinal cord	Receives information from the sensory organs and coordinates the response.
Peripheral nervous system	Network of nerves (neural network)	Carries signals from the body to the CNS and commands from the CNS to the body.

The brain: voluntary and involuntary actions

The brain coordinates both kinds of action.

Action	Control	Examples
Voluntary	We choose it (conscious).	Dancing, observing, eating
Involuntary	It happens without thinking (unconscious).	Heartbeat, breathing, digestion, blood circulation

Three pictures of involuntary actions: heartbeat, breathing and digestion — Involuntary actions.

Figure: Science Year 6 textbook, p.23.

The path of a signal in a voluntary action, such as seeing a flower:

Flow: stimulus (flower), detected by the eyes, sends a signal to the brain, produces a response — Stimulus, then sensory organ, then brain, then response.

Figure: Science Year 6 textbook, p.22.

The spinal cord and reflex actions

The spinal cord is joined to the brain. It carries information from the whole body to the brain and from the brain to the whole body. It also controls some reflex actions.

A reflex action is a quick, unconscious response. The spinal cord sends the command, so the signal does not wait to go to the brain first.

Reflex actions: stepping on a sharp object, sneezing when dust enters the nose, touching a hot object — Examples of reflex actions.

Flow: sharp object, detected by the foot, sends a signal to the spinal cord, produces a response — Stimulus, then sensory organ, then spinal cord, then response.

Figures: Science Year 6 textbook, p.24.

In a voluntary action the signal goes through the brain. In a reflex action the spinal cord gives the command. A signal can travel several hundred kilometres per hour, so both are fast.

The peripheral nervous system

The nerves outside the brain and spinal cord carry signals from the body to the CNS and command signals from the CNS to the rest of the body. If it is damaged, signals are disturbed:

Bell's palsy: the nerves to the face muscles are damaged. One side of the face droops, and it is hard to smile or close the eye.
Body imbalance: damaged nerves in the legs make the body lose balance and fall.

Taking care of the nervous system

What to do	Why
Eat a balanced diet	Vitamin B complex and minerals are good for the nerves.
Avoid alcoholic drinks	They slow down the signals in the nervous system.
Sleep seven to eight hours a day	It strengthens the neural network and memory.
Wear protective gear, such as a helmet	It prevents brain damage in an accident.
Keep good posture	It avoids damage to the nervous system.

Name the part of the nervous system that makes you pull your hand away from a hot cup.

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The spinal cord (a reflex action, part of the central nervous system).