Section 6- cell division and cellular organisation

seven specialised cells

• neutrophils

• squamous epithelial cells

• Guard cells/stomata

• Erythrocytes

• Soerm cells

• Palisade cells

• Root hair cells

Neutrophils

• Very flexible shape and lobed nucleus allows them to squeeze through cell junctions/fenestrations

• Form pseudopodia (cytoplasmic projections)) that engulf microorganisms

• Large number of lysosomes to ingest and destroy cells

Squamous epithelial cells

• A single layer of flattened cells

• The layer of cells form a thin-cross section which is permeable, so reduces diffusion pathway

Guard cells/stomata

• Inner cell walls are thicker which allows the cell to bend when turgid

• Cytoplasm has lots of chloroplasts and mitochondria

• In light, they pump in ions (active transport) which lowers the water potential, so water moves in by osmosis and the stoma opens

Erythrocytes

• Biconcave shape allows them to fit through the narrow capillaries

• No nucleus or organelles so more space for oxygen

Sperm cells

• Male gamers as haploid cells (23)

• Contain enzymes in the acrosome (head) to digest the cell wall of the female egg

• Lots of mitochondria for energy

• Have a flagellum (tail) to swim to the egg

• Aerodynamic to swim to egg faster

Palisade cell

• Large number of chloroplasts to maximise the absorption of life for photosynthesis

• Tall and thin, allows light to penetrate deeper before encountering another cell wall

• Walls are thin so carbon dioxide can easily diffuse into the cell

Root hair cell

• Mini micro hairs increase SA so the rate of water uptake by osmosis is greater (absorption)

• Thinner walls so water and mineral ions can move through more easy (short diffusion path)

• Mitochondria for active transport

Tissue

A group of differentiated similar cells that have specialists functions

Organ

Collection of tissues that are adapted to carry out a particular function

Organ system

Each system has a number of organs to carry out the major function of the organisms

Main types of animal tissues

• Nervous tissue

• Epithelial tissues

• Muscle tissues

• Connective tissue

• Epidermis tissue

• Vascular tissue

Nervous tissue

Support the transmission of electrical impulses

Epithelial tissue

Cover body surfaces- internal and external

Muscle tissues

contract (shorten) to move

Connective tissue

Either to hold other tissues together or acts as a transport medium

Epidermis tissue

Adapted to cover plant surface

Vascular tissue

Adapted for transport of H₂O and mineral ions

four stages of the cell cycle

G₁(gap phase), S-synthesis stage, G₂(gap phase), M- mitotic phase

G₁

cell grows, makes more organelles e.g. mitochondria, enzymes, proteins(transcription, translation), checks DNA code

S stage

semi-conservative replication, includes histone proteins, quick stage

why is the S stage quick?

to prevent mutations

G₂ phase

continued growth, increase glycogen stores(energy)

Mitotic phase

nuclear division and cytokinesis(cytoplasm splits)

mitosis- prophase, metaphase, anaphase, telophase

what stage happens after cytokinesis?

G₀

G₀ phase

cells can re-enter G₁ OR this is the stage for non-dividing cells such as highly specialised cells e.g. nerve cells or erythrocytes or the cell is simply too old to divide

what stages have checkpoints?

• end of G₁

• end of G₂

• mitotic phase

checkpoint in G₁

checks DNA errors- TP53 checks for mutations

checkpoint in G₂

check DNA for mutations- repairs cell if damaged but if cannot repair it apoptoses (programmed cell death)

checkpoint in mitotic stage

checks spindle fibres are correctly formed, prevents aneuploidy (e.g. Down syndrome)

why do cells divide?

growth, repair and replace

what stage do cells spend most of their time in?

interphase (G₁,S,G₂)

mitosis

the process of nuclear division that occurs before a cell physically divides in two

four stages of mitosis

PMAT

1. prophase

2. metaphase

3. anaphase

4. telophase

prophase

• chromosomes become visible (coil up, shorten, thicken, take stain more intensely)

• the nuclear envelope disintegrates

• nucleus becomes less prominent

• the centriole divides and move to the poles of the cell

• spindle fibres begin to form

metaphase

• each centriole is at a pole

• spindle fibres attach to the centromere of the chromosomes

• each centromere is attached to both poles

• chromosomes align along the metaphase plate/equator

anaphase

• spindle fibres contract and shorten

• the centromere divides

• chromatids(daughter chromosomes) are pulled to opposite poles of the cell

• each half of the cell receives one chromatid fro each chromosome

telophase

• chromatids reach the poles of the spindles

• they begin to uncoil

• they become less distinct

• nuclear envelope starts to reform

cytokinesis in animal cells

cell membrane constricts from the edges of the cell- cleavage furrow forms

cytokinesis in plant cells

carbohydrate rich vesicles form along the middle of the cell- a cell wall is laid down called the cell plate

asexual reproduction in yeast

parent cell develops an outgrowth or bulge-nucleus divides- one of the daughter nuclei migrates into the bulge- the bulge then grows to full size and detaches from parent cell

asexual reproduction in bacteria

divides by binary fission- chromosomal DNA is much quicker to copy(not in nucleus, one single loop)-daughter cells are genetically identical

when is asexual reproduction beneficial

when there is plentiful resources and conditions are favourable

what is bad about asexual reproduction

resources will become exhausted and a change in conditions will lead to death in population

what type of reproduction is mitosis in animals, plants and fungi?

asexual reproduction

significance of meiosis in life cycles

to produce haploid cells and genetic variations by independent assortment and crossing over