Biology: Cells, Body Systems and Reproduction
Cells, body systems and reproduction, for 13+ Biology, covers the basic structure of animal and plant cells (the organelles each contains and what each one does), the skeletal and muscular systems that let the body move, and how humans reproduce.
Before you start
Make sure you're comfortable with these topics first:
Method
- Learn the functions of the main organelles found in an animal cell (nucleus controls the cell and holds genetic material, cytoplasm is where chemical reactions happen, cell membrane controls what enters and leaves, mitochondria release energy) and the three extra structures a plant cell has (cell wall for support, chloroplasts for photosynthesis, a large permanent vacuole for storage).
- Learn the functions of the skeleton: support (holding the body upright), protection (of organs such as the brain and heart), movement (bones act as levers that muscles pull on), and production of blood cells (in the bone marrow).
- Learn the three main joint types and where each is found: hinge joints (elbow, knee) move in one plane only, ball-and-socket joints (hip, shoulder) allow rotation in multiple directions, and pivot joints (top of the neck) allow turning.
- Understand that a muscle can only actively contract and pull, never push, so joints are moved by antagonistic pairs of muscles working against each other; be able to state which muscle contracts and which relaxes to bend or straighten a named joint.
- Learn the names and basic functions of the main parts of the male reproductive system (testes produce sperm, sperm duct carries sperm, penis) and the female reproductive system (ovaries produce eggs, oviduct/fallopian tube is where fertilisation happens, uterus is where a foetus develops).
- Learn the sequence from fertilisation to birth: fertilisation happens in the oviduct, the fertilised egg implants in the lining of the uterus, the placenta and umbilical cord exchange oxygen, nutrients and waste between mother and foetus, and human gestation lasts approximately 40 weeks.
- Learn that puberty is the stage where the reproductive organs mature and physical changes appear, triggered by hormones, and be able to list changes typical of each sex.
- Always link a body structure to its precise function rather than describing it vaguely; for example write 'the placenta allows oxygen and nutrients to pass from mother to foetus' rather than just 'it helps the baby'.
Worked example
Explain how the structure of the elbow joint allows the arm to bend and straighten, referring to the biceps and triceps muscles.
- Identify the joint type: the elbow is a hinge joint, so it allows movement in one plane only, like a door hinge.
- Recall that a muscle can only contract (pull), never push, so bending and straightening a joint needs a pair of muscles working against each other (an antagonistic pair).
- To bend the arm, the biceps (at the front of the upper arm) contracts and shortens, pulling the forearm upward, while the triceps relaxes at the same time.
- To straighten the arm again, the triceps (at the back of the upper arm) contracts and shortens, pulling the forearm down, while the biceps relaxes.
- Final answer: the elbow is a hinge joint moved by the antagonistic pair of biceps and triceps; the biceps contracts while the triceps relaxes to bend the arm, and the triceps contracts while the biceps relaxes to straighten it, since a muscle can only pull and never push.
Practice questions
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Q1Name the organelle in a plant cell that contains chlorophyll and is the site of photosynthesis.Show answer
Answer: Chloroplast (chloroplasts)
Q2State two functions of the human skeleton.Show answer
Answer: Any two of: support (holding the body upright), protection (of organs such as the brain or heart), movement (bones act as levers for muscles), or production of blood cells (in the bone marrow)
Q3Name the joint type found in the hip, and state one other place in the body where this same joint type is found.Show answer
Answer: Ball-and-socket joint; also found in the shoulder
Q4Name the male gamete and the female gamete involved in human reproduction.Show answer
Answer: Sperm (cell) and egg (cell, or ovum)
Q5State the name of the structure that allows oxygen and nutrients to pass from a mother's blood to her developing foetus.Show answer
Answer: Placenta
Q6A doctor records that a foetus is 38 weeks old. Given that human gestation lasts approximately 40 weeks, state approximately how many weeks of pregnancy remain.Show answer
Answer: About 2 weeks
Q7Explain why muscles must work in antagonistic pairs rather than alone.Show answer
Answer: Because a muscle can only actively contract and pull a bone, not push it back, so a second muscle on the opposite side of the joint is needed to move the joint back the other way
Exam-style questions
Written in the style of a 13+ Common Entrance exam paper, with a full mark scheme.
(a) Name the joint type found at the knee. (b) State one way this joint type differs from a ball-and-socket joint. (c) Name the muscle at the front of the thigh, and the muscle at the back of the thigh, that work as an antagonistic pair to bend and straighten the knee.
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A pupil is researching the female menstrual cycle. (a) State the approximate length, in days, of an average menstrual cycle. (b) Name the female organ that releases one egg cell approximately once a month. (c) Explain what happens to the lining of the uterus if the egg released that month is not fertilised.
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State two physical changes that happen during puberty in boys, and two physical changes that happen during puberty in girls.
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Free printable worksheet
Want more practice on paper? Download the biology: cells, body systems and reproduction worksheet pack - 14 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 2 of 13+ Science Workbook, the whole course as one free printable PDF.
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