1.7Cell Structure and Molecular Biology
Cell division — EST 2 Biology Revision Notes & Topical Questions
5 min read 9 parts Lesson 7 of 11 2 quizzes
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
SAT Biology cell division: connect the cell cycle, mitosis and meiosis to growth, repair, gamete production and genetic variation. The cell cycle includes G1, S and G2 of interphase, followed by mitosis and cytokinesis.
- sister chromatids
- meiosis II
- Cytokinesis divides the cytoplasm. An animal cell forms a cleavage furrow that pinches the cell into two daughter cells
Section 1 of 9Cell cycle and checkpoints
1
G1, S and G2
The cell cycle includes G1, S and G2 of interphase, followed by mitosis and cytokinesis. In G1 the cell grows, in S phase DNA is replicated, and in G2 organelles and other components are prepared for division.
2
Checkpoints use internal regulators and external signals such as growth factors to determine whether division should continue. Cells with damaged DNA may stop, enter G0 or die; failure of regulation can contribute to cancer.
Section 2 of 9Chromosomes and preparation
Sister chromatids
After DNA replication, each chromosome consists of two identical sister chromatids joined at a centromere. Most of the life of a dividing cell is spent in interphase, when chromatin is extended and the nuclear envelope remains intact.
Mitosis divides the nucleus and preserves chromosome number. It supports growth, development and tissue repair and normally produces two diploid daughter cells genetically identical to the parent cell.
Section 3 of 9Stages of mitosis
1Prophase
In prophase chromosomes condense, the spindle forms and the nuclear envelope breaks down. In metaphase chromosomes align single file at the cell equator with spindle fibres attached to their centromeres.
2Anaphase
In anaphase sister chromatids separate and move to opposite poles. In telophase chromosomes decondense and new nuclear envelopes form around the two chromosome sets.
Section 4 of 9Cytokinesis
Cytokinesis
Cytokinesis divides the cytoplasm. An animal cell forms a cleavage furrow that pinches the cell into two daughter cells.
A plant cell builds a cell plate between the daughter nuclei. The plate develops into new cell walls, while a middle lamella helps keep neighbouring daughter cells attached.
Section 5 of 9Meiosis and variation
Meiosis I
Meiosis produces haploid gametes from a diploid parent cell. In meiosis I, homologous chromosomes pair, crossing-over can exchange genetic material, and homologous pairs separate to halve chromosome number.
Meiosis II
In meiosis II, sister chromatids separate. Crossing-over and independent alignment generate variation, so one diploid parent cell produces four genetically different haploid cells.
Section 6 of 9Cell-cycle checkpoints
1Checkpoints
Cells pass through checkpoints before progressing to the next stage of the cell cycle. These checks help ensure that the cell is large enough, has the nutrients it needs, and has copied its DNA accurately before division.
2
If serious damage is detected, progression can be delayed while the cell attempts repair. This reduces the chance of passing damaged DNA to daughter cells.
Section 7 of 9Cyclins and CDKs
Cyclins
Cyclins are proteins whose concentrations rise and fall through the cell cycle. They bind to cyclin-dependent kinases (CDKs). The resulting complexes activate proteins needed to move into the next stage.
CDKs are enzymes that remain largely inactive until a suitable cyclin binds. Their activity helps coordinate the timing of growth, DNA replication and cell division.
Section 8 of 9When regulation fails
Mutations that overactivate division-promoting genes or disable tumour-suppressing genes can let cells divide when they should stop. The resulting uncontrolled division can contribute to cancer.
Apoptosis
Cells with dangerous DNA damage may instead undergo apoptosis, a controlled form of programmed cell death. This removes cells that could otherwise cause harm.
Section 9 of 9Apoptosis in development
1
Apoptosis also shapes normal developing tissues. In an embryo, cells in the webbing between developing fingers are removed by programmed cell death, allowing separate fingers to form.
2Check:
Check Why is the removal of cells between the embryonic fingers useful? Answer: Programmed cell death removes tissue that is no longer needed and helps form distinct digits.
Marked practiceQuizzes for this lesson
Last updated:
Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.