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B12.1 Types of Reproduction

GCSE Combined Science · AQA · Chapter B12: Reproduction

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: asexual and sexual reproduction, gametes, pollination, twins and clones. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Describe asexual reproduction: one parent, no gametes, mitosis only, offspring are clones
  • Describe sexual reproduction: two parents, gametes made by meiosis fuse, offspring show variation
  • Name the gametes in animals and in flowering plants, and tell self-pollination from cross-pollination
  • Explain how identical and non-identical twins form
  • Calculate how fast a population grows by repeated doubling

Key words

  • Asexual reproduction: Reproduction involving one parent and no fusion of gametes. The offspring are genetically identical to the parent.
  • Sexual reproduction: Reproduction where a male and a female gamete fuse, so genetic information from two parents is mixed.
  • Gamete: A sex cell: sperm and egg cells in animals; pollen and egg cells in flowering plants.
  • Fertilisation: The fusion of a male gamete and a female gamete to make a zygote.
  • Clone: An organism that is genetically identical to another organism.
  • Binary fission: The way bacteria reproduce asexually: one cell splits into two identical cells.
  • Cross- pollination: Pollen from one plant fertilises an egg cell of a different plant of the same species.

Asexual reproduction

In asexual reproduction there is one parent and no fusion of gametes. There is no mixing of genetic information, so the offspring are genetically identical to the parent and to each other: they are clones. Only mitosis is involved.

  • Bacteria; How it reproduces asexually split into two identical cells by binary fission
  • Spider plant, strawberry; How it reproduces asexually grow runners with small plantlets that root in the soil
  • Tulip, onion; How it reproduces asexually form new bulbs underground
  • Dahlia, potato; How it reproduces asexually grow new plants from tubers
  • Starfish, some worms; How it reproduces asexually a broken-off piece can grow into a whole new animal

Exam tip: Clones share identical genes but can still look different, because the environment (light, food, injuries) also affects them.

Sexual reproduction

In sexual reproduction a male gamete and a female gamete fuse at fertilisation. The gametes are made by meiosis, so each carries half of the parent's genetic information. The offspring get a mixture of genetic information from two parents, which produces variation.

  • Animals; Male gamete sperm cell; Female gamete egg cell (ovum)
  • Flowering plants; Male gamete pollen (carries the male nucleus); Female gamete egg cell (inside the ovule)

In flowering plants, an insect or the wind carries pollen. Self-pollination: pollen fertilises egg cells of the same plant. Cross-pollination: pollen fertilises egg cells of a different plant. Both are sexual reproduction, because gametes made by meiosis fuse.

Twins

Identical twins form when one egg is fertilised by one sperm and the zygote splits into two. The twins have the same genes: they are clones of each other, but not of their parents. Non-identical twins form when two eggs are released and fertilised by two different sperm, so they are as different as any brothers and sisters and can be different sexes.

Worked example: classify it

A gardener takes a cutting from a geranium and grows it into a new plant. Which type of reproduction is this, and how will the new plant compare with the parent?
One parent, no gametes fuse, only mitosis: so it is asexual and the new plant has exactly the same genes.

Answer: asexual; a genetically identical clone

How fast asexual populations grow

If every cell divides into two each time, the number of cells doubles. After n divisions one cell has become 2ⁿ cells.

Worked example: bacteria doubling

One bacterium divides every 25 minutes in a warm wound. How many bacteria are there after 2 hours 30 minutes?
Time = 150 minutes. Number of divisions = 150 ÷ 25 = 6.
Number of bacteria = 2⁶ = 64.

Answer: 64 bacteria

Exam tip: Find the number of divisions first (total time ÷ time per division, in the same units), then work out 2ⁿ.

Common mistakes

  • Saying asexual reproduction uses meiosis. Only mitosis is involved.
  • Calling pollen the female gamete. Pollen carries the male gamete.
  • Thinking self-pollination is asexual. Gametes still fuse, so it is sexual reproduction.
  • Saying identical twins are clones of their parents. They are clones of each other only.
  • Thinking clones must look exactly alike. The environment can still make them different.

Revision questions

Try these, then check your answers below each one.

Question 1. Which statement correctly describes asexual reproduction? (Choose from: One parent, no gametes fuse, and the offspring are clones, Two parents, gametes fuse, and the offspring vary, One parent, and gametes made by meiosis fuse, Two parents, and the offspring are clones of both.)

Answer: One parent, no gametes fuse, and the offspring are clones

Working: Asexual reproduction needs only one parent and no fusion of gametes. Only mitosis is involved, so the offspring are genetically identical clones.

Question 2. The diagram shows two ways that twins can form. Which diagram shows how identical twins form? (Choose from: X, Y, both X and Y, neither.)

Answer: X

Working: In X one egg is fertilised by one sperm and the zygote splits into two, so both twins have the same genes. In Y two eggs are fertilised by two different sperm, giving non-identical twins.

Question 3. True or false? When a bee carries pollen from one apple tree to another apple tree, the trees are reproducing asexually.

Answer: False

Working: Pollen carries the male gamete, which fuses with an egg cell. This is cross-pollination, a form of sexual reproduction.

Related lessons

Continue in the full course

This lesson is section B12.1 (AGCSC1201) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.

 

 

 

 

 

 

 

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