13.3 The Best of Both Worlds

A free GCSE Biology lesson for AQA (8461) from OBA School: advantages and disadvantages of sexual and asexual reproduction; organisms that use both. 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

• Give the advantages of sexual reproduction, including variation and selective breeding
• Give the advantages of asexual reproduction
• Describe how malaria parasites, fungi and plants use both types of reproduction
• Evaluate which type of reproduction suits an organism in given conditions

Key words

• Variation: Differences between individuals. In a changing environment, variation means some individuals are likely to survive.
• Natural selection: Individuals best suited to their environment are more likely to survive, breed and pass on their alleles.
• Selective breeding: Humans choose parents with useful characteristics and breed them, generation after generation.
• Spore: A small reproductive cell (for example, from a fungus) that can grow into a new organism.
• Vector: An organism that carries a pathogen from one host to another, e.g. the mosquito for malaria.
• Runner: A side stem that grows along the ground and forms new plantlets (asexual).

Advantages of sexual reproduction

• It produces variation in the offspring.
• If the environment changes (a new disease, a colder climate, a new predator), variation makes it likely that some individuals survive. This gives a survival advantage through natural selection.
• Humans can use it in selective breeding, which speeds up the selection of useful features, for example to increase food production.

Disadvantages: it needs two parents, so time and energy are spent finding and attracting a mate (or, in plants, on flowers and pollinators). It is slower, and fewer offspring are made.

Worked example: a changing environment

A new virus infects a population of wild rabbits. Explain why some rabbits survive.
Sexual reproduction has produced variation. Some rabbits happen to have alleles that give resistance. They survive and breed, passing these alleles on.

Answer: variation means some individuals are resistant

Advantages of asexual reproduction

• Only one parent is needed: no mate has to be found.
• It is more time- and energy-efficient.
• It is faster than sexual reproduction.
• Many identical offspring can be made quickly when conditions are good, so the organism can spread fast.

Disadvantage: there is no variation. If conditions change, for example a new disease arrives, the whole population may be wiped out.

Exam tip: In "evaluate" questions give advantages and disadvantages of each, then finish with a judgement: which type is better in that situation, and why.

Organisms that use both

Some organisms get the best of both worlds: they reproduce asexually to multiply quickly, and sexually to create variation.

• Malaria parasite; Asexual in the human host (in liver cells and red blood cells); Sexual in the mosquito
• Many fungi; Asexual by spores made by mitosis; Sexual make spores by meiosis that give variation
• Many plants; Asexual runners (e.g. strawberry plants), bulb division (e.g. daffodils); Sexual flowers make gametes; seeds form after fertilisation

Exam tip: Inside the human the parasite multiplies fast by asexual reproduction. Its gametes meet inside the mosquito, so sexual reproduction happens there.

Weighing up the evidence

Worked example: using data (maths skill)

A gardener grows new strawberry plants in two ways. Of 50 plants grown from runners, 46 survive. Of 200 seeds sown, 118 grow into plants.
Runners: 46 ÷ 50 × 100 = 92% survival. Seeds: 118 ÷ 200 × 100 = 59% success.
Runners give a higher success rate and plants identical to a good parent. Seeds give variation, which might include new, useful features.

Answer: runners 92%, seeds 59%

Common mistakes

• Saying malaria parasites reproduce sexually in humans. It is the other way round: asexually in humans, sexually in the mosquito.
• Writing "sexual reproduction is better" without saying when or why. The best method depends on the conditions.
• Saying asexual reproduction gives variation. Offspring are clones; any differences come from the environment.
• Forgetting the link: variation → some survive a change → natural selection.

Revision questions

Try these, then check your answers below each one.

Question 1. Where does the malaria parasite reproduce sexually? (Choose from: In the mosquito, In human red blood cells, In the human liver, In pond water.)

Answer: In the mosquito

Working: Malaria parasites reproduce asexually in the human host (liver and red blood cells) and sexually in the mosquito.

Question 2. True or false? Asexual reproduction is faster than sexual reproduction and needs only one parent.

Answer: True

Working: True. No mate has to be found, so asexual reproduction is quicker and more time- and energy-efficient.

Question 3. Which is an advantage of sexual reproduction? (Choose from: It produces variation, so some offspring may survive if the environment changes, Only one parent is needed, Offspring are identical to a successful parent, It uses less time and energy.)

Answer: It produces variation, so some offspring may survive if the environment changes

Working: Sexual reproduction gives variation, which gives a survival advantage by natural selection if conditions change.

Related lessons

• Previous lesson: 13.2 Cell Division in Sexual Reproduction
• Next lesson: 13.4 DNA and the Genome
• In this chapter: 13.1 Types of Reproduction
• In this chapter: 13.5 DNA Structure and Protein Synthesis
• In this chapter: 13.6 Gene Expression and Mutation

Continue in the full course

This lesson is section 13.3 (AGCBH1303) of our free GCSE Biology 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 Biology course.