Section 6 - Cell Division and Cellular Organisation

What is the cell cycle and how does it start and end?

The process all body cells use to grow and divideIt starts when a cell is produced by cell division and ends when the cell divides to produce two new cells

What are the two periods of cell division

Interphase - cell growth and DNA replication M phase - cell division ( mitosis - nuclear division and cytokensis - cytoplasmic division)

What are the divisions of interphase

G1, S and G2

So what is the overall order of the cell cycle

G1 S G2 M

What happens in Gap Phase 1

The cell grows and new organelles and proteins are made

What happens in G1 checkpoint

The cell checks the chemicals needed for replication are present and for any damage to the DNA before entering s phase

What happens during synthesis

The cell replicates its DNA, ready to divide by mitosis

What happens in the Gap phase 2

Cells keep growing and proteins needed for division are made

What happens in the G2 checkpoint

The cell checks weather all the DNA has been replicated without any damage. If it has, the cell can enter mitosis

What happens to the cell during interphase

The cells DNA is unravelled and replicated, to double its genetic content The organelles are also replicated so it has spare ones and its ATP content is increases

What is the difference between meiosis and mitosis

Mitosis produces two genetically identical “daughter” cells from a single “parent” cell, whereas meiosis produces cells that are genetically unique from the parent and contain only half as much DNA

What are the four stages of mitosis

Prophase Metaphase Anaphase Telophase

What is the structure of chromosomes in mitosis

The chromosomes are made of two strands joined together by a CENTROMERE, The separate strands are called sister chromatids There are two strands because each chromosome has made an identical copy of itself during interphase

Describe what happens in PROPHASE

The chromosomes condense getting shorter and fatter The centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle The nuclear envelope breaks down and chromosomes lie free in the cytoplasm

Describe what happens in METAPHASE

The chromosomes become attached to the spindle fibres by their centromereThey line up along the middle of the cell at the spindle equatorAt the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue

Describe what happens in ANAPHASE💗

The centromeres divide, separating each pair of sister chromatids The spindles contract, pulling chromatids to opposite ends of the cells, centromeres first

Describe what happens in Telophase

The chromatids reach the opposite poles on the spindleThey uncoil and become long and thin again - they are now called chromosomes again. A nuclear envelope forms around each group of chromosomes so there are now two nuclei

Describe what happens in cytokinesis and when does it usually begin and end

The cytoplasm divides - cytokinesis usually begins in anaphase and ends in telophase

What is the difference between cytokinesis in animals and plant cells

In animal cells, a cleavage furrow forms in the cytoplasm In plant cells, cytokinesis it occurs with the formation of a cell plate in the middle of the cell

Label each line with which stage the cell is going through

What stage are all these cells undergoing

PROPHASE

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Metaphase

What stage are these cells undergoing

Anaphase

"What stage are these cells undergoing

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TELOPHASE

Fill in the gap - _ are the sperm cells in males and egg cells in females. In sexual reproduction ____ ___ join together at __ to form a ___

GametresTwo GametesFertizilation Zygote

How many chromosomes do normal body cells have?

The diploid number of chromosomes - each cell contains two of each chromosome (a pair) one from mum and one from dad

What are pairs of matching chromosomes called?

Homologous chromosomes - they are the same size and have the same gene although they could be alleles

How many chromosomes do gametes have

A haploid number

What happens at fertilisation?

A haploid sperm fuses with a haploid egg making a cell with the normal diploid number of chromosomes.The diploid cell produced is a zygote

What is meiosis

"A type of cell division in reproductive organs to produce gametes. Cells that divide by meiosis are diploid to start with but the cells that are formed are haploid. Cells formed by meiosis are genetically different because each new cell ends up with a different combination of chromosomes

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What happens during interphase in meiosis

The cell's dna unravels and replicates to produce double-armed chromosomes called sister chromatids

What does meiosis involve?

2 divisions - meiosis 1 and 2 and after interphase cells enter 1

What happens in prophase 1?

The chromosomes condense, becoming shorter and fatter Homologous chromosomes pair up - number 1 with number 1, 2 with 2 e.t.c Crossing over occurs and the centrioles start moving to opposite ends of the cell, forming the spindle fibres The nuclear envelope starts to break down

What happens in metaphase 1

The homologous pairs attach to the spindle fibres by their centromeres and line up across the centre of the cell

What happens in anaphase 1

The spindles contract, pulling pairs apart to opposite poles of the cell

Explain what happens in telophase 1

A nuclear envelope forms around each group of chromosomes. Cytokinesis occurs and two haploid daughter cells are produced.

What happens in meiosis 2

The two daughter cells undergo pmat 2, but in anaphase 2 the sister chromatids are seperatedFour haploid cells are produced

What is genetic variation and how does meiosis create this?

The differences that exist between individual's genetic material. meiosis creates this as it makes gametes that are all genetically different. Then in fertilisation any egg can fuse with any sperm

What is the first event in meiosis that causes genetic variation?

Crossing over of chromatids:During prophase 1, the homologous pairs of chromosomes come together and pair up The chromatids twist around eachother and bits of chromatids swap over. The chromatids still contain the same genes but now have a different combination of alleles

What is event 2 in meiosis that causes genetic variation

Independent assortment

What is independent assortment?

Each homologous pair of chromosomes is made up of one chromosome from your mum and one chromosome from your DadWhen the pairs line up in metaphase 1, its completely random which chromosomes from each pair end up in which daughter cell. This means the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.

What are stem cells

Unspecialised cells that can develop into different types of cell's - all multicellular organisms stem from stem cells

Where are stem cells found in humans?

In early embryos

Describe differentiation

The process by which a cell becomes specialised for its job

Explain an example of how adult stem cells are used

They are used to replace damaged cells The main bones of the body have bone marrow in the centre. Here, adult stem cells divide and differentiate to replace worn out blood cells - erythrocytes (red blood cells) and neutrophils (WBC)

Why is mitosis significant in life cycles?

GrowthTissue repairAsexual reproduction in plants, animals and fungi

Where are the stem cells found in plants and how do they work?

In plants, stem cells are found in the meristem. In the root and stem, stem cells of the vascular cambium (vascular bundle) divide and differentiate to become xylem vessels and phloem sieve tubes.

How can stem cells be used in medicine?

To repair damaged tissues (like in the heart)Treatment of neurological disorders Research of developmental biology Bone marrow transplants

How are erythrocytes specialised for their function?

They carry oxygen in the blood. The biconcave disc shape provides a large surface area for gas exchange. They have no nucleus so there's more room for haemoglobin Small so can fit through capillaries and get close to respiring cells

How are neutrophils specialised for their function?

They defend the body against disease. Their flexible shape allows them to engulf foreign particles or pathogens The many lysosomes in their cytoplasm contain digestive enzymes to break down the engulfed particles.

How are epithelial cells specialised for their function?

They cover the surfaces of organs. The cells are joined by interlinking cell membranes and a membrane at their base. Ciliated epithelia have cilia that beat to move particles away. Other epithelia have microvilli folds in the cell membrane that increase the cell's surface area. Squamous epithelia are very thin to allow efficient diffusion of gases.

How are sperm cells specialised for their function?

They have a flagellum (tail) so they can swim to the egg (female sex cell). They also have lots of mitochondria to provide the energy to swim. The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg.

How are palisade mesophyll cells specialised for their functions?

They do most of the photosynthesis. They contain many chloroplasts, so they can absorb a lot of sunlight. The walls are thin, so carbon dioxide can easily diffuse into the cell.

How are root hair cells specialised for their function?

They absorb water and mineral ions from the soil. They have a large surface area for absorption and a thin, permeable cell wall, for entry of water and ions. The cytoplasm contains extra mitochondria to provide the energy needed for active transport

How are guard cells specialised for their function?

Guard cells are found in pairs, with a gap between them to form a stoma. This is one of the tiny pores in the surface of the leaf used for gas exchange. In the light, guard cells take up water and become turgid. Their thin outer walls and thickened inner walls force them to bend outwards, opening the stomata. This allows the leaf to exchange gases for photosynthesis.

What is a tissue?

A group of cells that are specialised to work together to carry out a particular function

Explain the squamous epithelium tissue

It is a single layer of flat cells lining a surface that is found in many places in the body, including the alveoli in the lungs, provides a thin exchange surface for substances to diffuse across quickly

Explain the ciliated epithelium

It is a layer of cells covered in cilia Its found on surafaces where things need to be moved - e.g trachea

Explain the muscle tissue

Made up of bundles of elongated cells called muscle fibres There are three different types of muscle tissue : smooth (lining of stomach wall), cardiac and skeletal(which you use to move)

Explain cartilage

A type of connective tissue found in the joints It also shapes and supports the ears, nose and windpipe. Its formed when chondroblasts secrete an extracellular matrix (jelly subtance containing protein fibres) which they become trapped inside

Explain the xylem tissue

Has two jobs - transporting water around the plant, and it supports the plant. It contains hollow xylem vessel cells (dead) and living parenchyma cells

Explain the phloem tissue

Transports sugars around the plant. Arranged in tubes and made up of sieve cells, companioin cells and some ordinary plant cells Each sieve has end walls with holes in them (sieve plates), so that sap can move easily through them

Explain the lungs as an organ

Carry out gas exchange They contain squamous epithelium tissue (in the alveoli) and ciliated epithelium tissue (in the bronchi)They also have elastic connective tissue and vascular tissue ( in the blood vessels)

Explain the leaf as an organ

Carries out gas exchange and photsynthesisIt contains palisade tissue, epidermal tissue to prevent water loss and xylem and phloem tissues

Explain the respiratory as an organ system

Function is gas exchange

what are totipotent cells

Can form both embryonic and extra-embryonic (placental) cells

what are Pluripotent stem cells

Can develop into any cell type except placental cells

what are multipotent

Can develop into a limited range of cell types