What is cell division?
Cell division is the process where a parent cell splits into daughter cells. It enables growth, repair, and reproduction, occurring through mitosis for identical cells or meiosis for genetic diversity
What is mitosis?
Mitosis is used for growth and repair and produces two identical daughter cells
What is meiosis?
Meiosis produces our sex cells (sperm and ovum) for sexual reproduction
What are the phases of mitosis?
- prophase
- metaphase
- anaphase
- telophase
-cytokinesis
What is cytokinesis?
Cytokinesis is the process in cell division where the cytoplasm splits, creating two daughter cells. It follows mitosis or meiosis, ensuring each new cell has organelles and cytoplasmic contents
What is interphase?
Interphase is the longest stage in the eukaryotic cell cycle, during which the cell prepares for division. It consists of three phases:
- G1 phase: The cell grows and acquires nutrients.
- S phase: The cell replicates its DNA.
- G2 phase: The cell continues to grow and prepares for mitosis.
During interphase, the cell synthesizes proteins and organelles necessary for its function and division
Stages of mitosis?
Prophase → Chromosomes condense, spindle fibers form, nuclear membrane starts breaking down.
Metaphase → Chromosomes line up along the cell’s equator.
Anaphase → Sister chromatids separate and move to opposite poles.
Telophase → Nuclear membranes reform around chromosomes, which de-condense.
Cytokinesis → Cytoplasm divides, forming two daughter cells.
What are the stages of meiosis I?
Meiosis I (reduction division)
Prophase I → Chromosomes condense, homologous chromosomes pair (synapsis), crossing over occurs.
Metaphase I → Homologous pairs line up at the cell’s equator.
Anaphase I → Homologous chromosomes separate to opposite poles (sister chromatids stay together).
Telophase I → Nuclear membranes may reform; cytoplasm divides producing two haploid cells (each containing half the number of chromosomes as the original diploid cell)
What are the stages of meiosis II?
Meiosis II (equational division)
Prophase II → Chromosomes condense again, spindles form.
Metaphase II → Chromosomes line up individually at the equator.
Anaphase II → Sister chromatids separate and move to opposite poles.
Telophase II → Nuclear membranes reform; cytoplasm divides → four haploid daughter cells form.
What are homologous pairs?
Homologous pairs are pairs of chromosomes in a diploid cell that are the same size and shape, carry genes for the same traits at the same loci, but may have different alleles.
How is variation achieved?
Variation is achieved mainly through mutation, meiosis (independent assortment + crossing over), and random fertilisation, with environmental factors further shaping traits.
What is the law of independent assortment?
- Gregor Mendel’s law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another.
- this occurs during Metaphase I.
- chromosomes line up at the equator of the cell in a random arrangement.
What is crossing over in meiosis?
During meiosis, genetic information can be exchanged between homologous chromosomes in a process called crossing over.
Crossing over results in the recombination of alleles, ensuring every sperm and egg is unique
What is gametogenesis?
Gametogenesis is the process by which specialized sex cells (gametes) are produced in organisms.
- in males → spermatogenesis produces sperm.
- in females → oogenesis produces eggs (ova).
Gametogenesis involves meiosis, reducing the chromosome number by half to ensure haploid gametes.
What is the location of spermatogenesis?
Spermatogenesis describes the production of spermatozoa (sperm) in the seminiferous tubules of the testes
What is the process of spermatogenesis? (4)
- the process begins at puberty when diploid cells called spermatogonia undergo mitosis and cell growth to form spermatocytes.
- the spermatocytes undergo two meiotic divisions to form four haploid daughter cells (spermatids) with equal amounts of cytoplasm.
- the spermatids then undertake a process of differentiation to become functional sperm cells called spermatozoa
- the whole process takes approximately 70 days and is continuous
What is the process of oogenesis?
- Before birth
- In the ovaries, oogonia (diploid stem cells) multiply by mitosis.
- They develop into primary oocytes and start meiosis I but stop at prophase I until puberty. - Puberty → each menstrual cycle
- at puberty, hormones from the pituitary gland (FSH and LH) trigger some primary oocytes to resume meiosis I.
- Each produces:
–One secondary oocyte (haploid, large cytoplasm)
–One polar body (small haploid cell discarded in oogenesis) - Ovulation
- The secondary oocyte is released from the ovary.
- It starts meiosis II but stops at metaphase II. - Fertilisation
- If a sperm enters, the secondary oocyte completes meiosis II.
- Produces:
– One ovum (mature egg)
– Another polar body.
Summary:
- Oogenesis = process of forming eggs.
- Results in 1 functional ovum and 3 polar bodies from each primary oocyte (to conserve cytoplasm for the egg).
What is random fertilisation?
The process where any sperm can fuse with any egg, producing a zygote with a unique combination of genes. This adds to genetic variation in sexually reproducing organisms.
What is independent assortment?
During meiosis I, homologous chromosome pairs line up randomly at the cell’s equator. This means the maternal and paternal chromosomes are distributed independently into gametes, creating genetic variation.
What is asexual reproduction?
Reproduction with one parent, producing genetically identical offspring without gametes or fertilisation.
What is sexual reproduction?
Reproduction involving two parents, producing genetically unique offspring through the fusion of gametes (fertilisation).
What is a gamete?
A sex cell (sperm or egg) that is haploid (n) and can fuse with another gamete during fertilisation to form a zygote.
What is a locus?
The specific location of a gene on a chromosome. Each gene has a fixed locus that can have different versions called alleles.
What is an allele?
A variant form of a gene found at a specific locus on a chromosome. Different alleles can produce different traits (e.g., eye color).
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Unit 3 - Topic 1 (Biodiversity)39
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Unit 3 - Topic 1 (Classification Processes)42
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Unit 3 - Topic 2 (Functioning Ecosystems)34
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Unit 4 - Topic 1 (DNA structure and replication)23
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Unit 4 - Topic 1 (Cellular replication and variation)25
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Unit 4 - Topic 1 (Gene expression)38
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Unit 4 - Topic 1 (Mutations)26
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Unit 4 - Topic 1 (Biotechnology)19
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Unit 4 - Topic 1 (Inheritance)15
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Unit 4 - Topic 2 (Evolution)31
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meiosis - cellular replication extra7
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gene expression - extra12
