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Topic Three: Voice of the Genome

Feature Prokaryotic Cell Eukaryotic Cell

Animal Cell Plant Cell
Nucleus with envelope Absent Present Present
Membrane-bound organelles Absent Present Present
DNA found as A loop Separate strands Separate strands
Slime capsule Sometimes present Never present Never present
Flagellum Simple (if present) Complex (if present)…

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[INSERT REVISION ON GAMETES]

Fertilisation of the ovum:

1. Sperm reaches the ovum
2. Chemicals are released from the cells surrounding the
ovum, triggering to acrosome reaction
3. Acrosome swells and fuses with sperm cell surface
membrane
4. Digestive enzymes in acrosome released
5. Enzymes digest through follicle cells and…

Page 3

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Female plants - only one of the four nuclei forms an ovum at the end of meiosis (others
disintegrate)
Male plants ­ four haploid cells produced by meiosis undergo another division, mitosis. Each
nucleus divides to give two haploid nuclei within the pollen grain
(One is tube nucleus, controls development…

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Crossing over:

first meiotic division ­ homologous chromosomes come together as pairs and all four
chromatids come into contact
at contact the chromatids break and re-join, exchanging sections of DNA
the point where chromatids break is called a chiasma
several chiasmata occur along the length of each pair of chromosomes…

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Fertilisation in mammals:

nuclei from the gametes combine
nucleus from one sperm enters the ovum and their genetic material combines forming a
zygote (containing genetic material from both parents)

Fertilisation in flowering plants:

nuclei from the gametes combine
takes place in the embryo sac within the ovule
pollen grain germinates…

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the second fuses with two nuclei in the embryo sac (polar nuclei) to form a triploid cell
(seed's storage tissue ­ endosperm)

Cell Cycle
Interphase:

New cell organelles are synthesised and DNA replication occurs ­ preparation for division

A time of intense and organised activity
Cell synthesises new cell components…

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Process:



Individual chromosomes unravel




Allows access to the genetic material

enabling new proteins to be synthesised




Cell synthesises additional

Cytoplasmic proteins and organelles




Cell must also produce copies of the DNA

for the two new cells (DNA must be identical)



Cell Division:

Prophase:

1. Chromosomes condense and become visible as…

Page 8

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2. Fibres pull chromatids apart with the centromere leading

Telophase:

1. Chromosomes de-condense (become invisible)
2. Nuclear envelope reforms
3. Nucleolus reappears
4. Two sets of genetic information enclosed in separate nuclei

Cytoplasmic Division:

Animal cells ­ cell surface membrane constricts around the centre of the cell
Ring of protein…

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Sequence Reason Safety
Cut final 5mm of a root tip from This is where mitosis occurs Care when cutting
a plant (onion)

Page 10

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Add stain (orcein) and an acidThe acid softens the tissues Take care with the stain and
whilst the stain highlights acid (skin and eyes)
chromosomes
Gently break open on a Spreads out the cells and Careful not to break the glass
microscope slide and squash makes them one layer thick…

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