2.1.6 Cell division, cell diversity and cellular organisation

What are the phases of the cell cycle

• Interphase

• Mitosis (nuclear division)

• Cytokinesis (Cell division)

What are the 3 phases of interphase

• G1 Phase

• S Phase

• G2 Phase

What is the cell cycle

A highly ordered sequence of events that takes place in a cell, resulting the division of the cell, and the formation of two genetically identical daughter cells

What happens in G1 of interphase

First growth phase:

• Cells produce RNA, enzymes and other proteins required for cell growth

• Cell receives a signal to divide (progress into the S phase) - controlled by cyclins

What happens in the S phase of interphase

Synthesis of new DNA:

• DNA in the nucleus replicates - each chromosome contains two identical chromatids

What happens in G2 of Interphase

Second growth stage

• Newly synthesised DNA is checked for any errors

  • Normally repaired

    • If not then apoptosis (controlled cell destruction)

• Cell continues to increase in size

• Energy stores increased

• Tubulin made - needed for Mitosis

What is Mitosis

• Period of cell division in which the nucleus divides

• Consists of 4 stages: (PMAT)

  • Prophase

  • Metaphase

  • Anaphase

  • Telophase

What is mitosis used in

• Growth of multicellular organisms (animals, plants, fungi)

  • unicellular zygotes can grow into multicellular organisms

  • Continued cell division in the meristem of plants

• Replacement of cells and repair of tissues

  • Cell replacements in the skin and gut lining

  • Axolotls regenerating lost limbs and tails

• Asexual reproduction - reproduction with single parent organisms

  • Unicellular Amoeba, budding in plants (& yeast) & runners

What is a centrosome

• Organelle that becomes visible during mitosis

• Helping pair up and move chromosomes

• Contain 2 centrioles where spindle fibres emerge and attach to centromeres in the middle of chromatids (DNA molecules that make up DNA)

What happens in the Prophase stage of mitosis (4)

• Chromatin condenses - forming chromosomes that are joined together at the centromere

• Centrosomes move to opposite poles - spindle fibres emerge from them due to centrioles

• Spindle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell

• Nuclear envelope breaks down into vesicles + nucleolus disappears

What happens in the Metaphase stage of mitosis

• Chromosomes are lined up by the spindle fibres to form a plane at the equator (aka the metaphase plate)

• Spindle fibres attach to chromosomes and hold them in position

What happens in the Anaphase stage of mitosis

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What is a specialised cell

Cells that are differentiated to carry out very specific functions

What is an erythrocyte/red blood cell (function, location, adaptations)

Function:

• Transport oxygen around the body

Location:

• Produced in Bone marrow

• Circulate in bloodstream

Adaptations:

• Flattened, Biconcave shape - increases surface area to volume ratio

• Not many organelles + no nuclei to make space for haemoglobin

• High amounts of haemoglobin in the cytoplasm

• Flexible to squeeze through narrow capillaries due to elastic membrane

What is a neutrophils cell (function, location, adaptations)

Function:

• Destroy pathogens by phagocytosis and the secretion of enzymes

Location:

• Produced in Bone marrow

• Circulate in bloodstream

Adaptations:

• Multi lobed nucleus - makes it easier to squeeze through small gaps and get to the site of infection

• Flexible shape allows them to squeeze through cell junctions in the capillary wall

  • Also allows for pseudopodia: cytoplasmic projections that engulf microorganisms

• Granular cytoplasm contains many lysosomes that contain enzyme used to attack pathogens

What is a sperm cell/spermatozoa (function, location, adaptations)

Function:

• Reproduction - fuse with egg and initiate the development of an embryo and pass on fathers gene

Location:

• Produced in testes

Adaptation:

• Head contains a nucleus with half the normal number of chromosomes (haploid nucleus)

• Head contains acrosome’s that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus

• Mid-piece is packed with mitochondria to release energy for tail movement

• Tail rotates - propelling the sperm cell forwards and allowing it to move towards the egg

What is a root hair cell (function, location, adaptations)

Function:

• Absorption of water and mineral ions from soil

Location:

• Surface of plant roots

Adaptations:

• Has root hair to increase surface area of water uptake by osmosis is greater - can absorb more water and ions

• Thinner cell walls for shorter diffusion

• Permanent vacuole contains cell sap - more concentrated than soil water, maintaining a water potential gradient

• Mitochondria for active transport of mineral ions

• No chloroplasts as they’re underground

What is a palisade cell (function, location, adaptations)

Function:

• Carry out photosynthesis to produce glucose and oxygen

Location:

• Palisade mesophyll layer

Adaptations:

• Large number of chloroplasts present in the cytoplasm to maximise the absorption of light for photosynthesis

• The tall and thin shape allows light to penetrate deeper before encountering another cell wall + for many cells to be densely packed together

• Large vacuole to maintain turgid pressure

What is a Guard cell (function, location, adaptations)

Function:

• Control the opening of the stomata to regulate water loss and gas exchange

Location:

• Plant’s epidermis

Adaptations:

• Inner cell walls are thicker (those facing the air outside the leaf) while the outer cell walls are thinner

  • The difference in the thickness of the cell walls allows the cell to bend when turgid

• Cytoplasm has a high density of chloroplasts and mitochondria

  • May play a role in the opening of the stomata

What are Ciliated Epithelium (function, location, adaptations)

Function:

• Moving substances across the surface of a tissue

Location:

• Respiratory and female reproductive systems

Adaptations:

• Made up of cilia - beat in a coordinated way to shift material along the surface of the epithelium tissue

• Mitochondria to provide energy for movement

• Goblet cells secrete mucus which helps to trap dust, dirt and microorganisms - preventing them from causing infection

What is squamous epithelium cells (function, location, adaptations)

Function:

• Provide a surface covering or outer layer

• Present when rapid diffusions across a surface is essential

Location:

• Variety of organs + structures - blood vessels and alveoli

Adaptations:

• Single layer of flattened cells on a basement membrane

  • forms a thin cross-section which reduces the distance that substances have to move to pass through - shortens the diffusion pathway

• Permeable, allowing for the easy diffusion of gases

What is Phloem tissue (function, location, adaptations)

Function:

• Translocation of organic solutes (e.g. sucrose)

Location:

• Vascular bundles

Adaptations:

• Sieve tube elements with perforated sieve plates.

• Companion cells with many mitochondria for active loading.

• Plasmodesmata link companion cells to sieve tubes.

What is Xylem tissue (function, location, adaptations)

Function:

• Transport water and mineral ions

• Provide structural support

Location:

• Vascular bundles

Adaptations:

• Dead cells forming continuous tubes with no end walls.

• Lignified walls for strength and waterproofing.

• Pits allow lateral movement of water.

What is Muscle tissue (function, location, adaptations)

Function:

• Contraction to cause movement

Location:

• Skeletal muscles

• Heart

• Walls of organs

Adaptations:

• Long fibres containing actin and myosin

• Many mitochondria to supply ATP

• Can shorten and relax

What is cartilage tissue (function, location, adaptations)

Function:

• Provides flexible support and reduces friction at joints

Location:

• Joints

• Trachea

• Ear