What does diploid mean?

Containing two sets of chromosomes, one inherited from each parent.

How many chromosomes are there in a human body cell, and how many in a human gamete?

There are 46 in a body cell and 23 in a gamete.

Explain why a fertilised egg cell is diploid.

Two haploid gametes fuse, so their single sets of chromosomes combine to give two full sets.

A plant has 14 chromosomes in each of its leaf cells. How many chromosomes are in each of its pollen grain nuclei?

Seven, because gametes are haploid and carry half the number found in a body cell.

OCR GCSE Biology A J247

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition and trophic levels Pyramids of biomass and the efficiency of transfer

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Asexual and sexual reproduction compared Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination, multiple genes and Mendel's work Variation within a population, and classification Natural selection and evolution Evidence for evolution, and the work of Darwin and Wallace

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Food security, agricultural and biotechnological solutions Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples Physical and chemical plant defences White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc The eye and its common defects The structure and function of the brain Hormones and the endocrine glands Hormones in reproduction and the menstrual cycle Methods of contraception Tropisms, auxin and the roles of plant hormones Homeostasis, and the skin in temperature control Insulin and the control of blood glucose Type 1 and type 2 diabetes Osmotic changes in body fluids, and the kidneys Kidney structure and the parts of the tubule

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Genes, Inheritance and Selection

Haploid, diploid and meiosis

3 things to know
Paper 2

Overview

What haploid and diploid mean, human chromosome numbers in body cells and gametes, why a fertilised egg and an embryo's cells are diploid, how meiosis halves the chromosome number to make four gametes, how meiosis and fertilisation keep the number constant, meiosis as a source of variation, where it happens, and how it compares with mitosis.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how meiosis and fertilisation keep the chromosome number constant, why every gamete is genetically different, and how meiosis differs from mitosis.

Key term

What does haploid mean?

Key term

Which human cells are haploid?

Questions from this subtopic

Each one with the model answer underneath.

1
What does haploid mean?
Model answer
Containing a single set of chromosomes, that is one copy of each.
2
What does diploid mean?
Model answer
Containing two sets of chromosomes, one inherited from each parent.
3
Which human cells are haploid?
Model answer
The gametes, which are the sperm cells and the egg cells.
4
How many chromosomes are there in a human body cell, and how many in a human gamete?
Model answer
There are 46 in a body cell and 23 in a gamete.
5
Explain why a fertilised egg cell is diploid.
Model answer
Two haploid gametes fuse, so their single sets of chromosomes combine to give two full sets.
6
A plant has 14 chromosomes in each of its leaf cells. How many chromosomes are in each of its pollen grain nuclei?
Model answer
Seven, because gametes are haploid and carry half the number found in a body cell.

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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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