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What are the stages of the cell cycle?

Gap phase 1
G1 checkpoint
M phase
Gap phase 2
G2 checkpoint


G2 checkpoint

Cell checks whether all DNA has been replicated without any damage
If it had the cell can enter mitosis


M phase

Mitosis (nuclear division) and cytokinesis
(Cytoplasmic division) Metaphase checkpoint


Gap phase 1

Cell grows and new organelles and proteins are made


G1 checkpoint

Cell checks that the chemicals needed for replication are present and for any damage to the DNA before entering S-phase


Gap phase 2

Cell keeps growing and proteins needed for cell division are made



Cell replicated its DNA ready to divide by mitosis


When does the cell cycle start and end?

Starts When a cell has been produced by cell division
Ends with cell dividing to produce two identical cell


What does the cell cycle consist of?

Period of cell growth and DNA replication (interphase)
Periods of cell division (M phase)


What is interphase subdivided into?

Cell growth
Subdivided into three different separate growth stages
G1, s and G2


How is the cell cycle regulated?

By checkpoints that occur at key points during a cycle to make sure it's okay for the process to continue


What is mitosis needed for?

The growth of multicellular organisms (like us)
Repairing damaged tissues
Method of asexual reproduction for some plants, animals and fungi


What is mitosis really?

One continuous process
Series of division phases: prophase, metaphase, anaphase and telophase


When does interphase happen?

Before mitosis in the fell cycle
When the cell grows and replicates their DNA ready for division


Describe interphase

Cell carried out normal functions and prepares to divide
Cells DNA is unraveled and replicated to double its genetic content
Organelles replicated so it has spare ones
ATP is increased (ATP provides energy needed for cell division)


Describe prophase?

Chromosomes condense getting shorter and fatter
Tiny bundled of protein (centrioles) start moving to opposite ends of cell forming network of protein fibres (spindle)
Nuclear envelope breaks down and chromosomes lie free in the cytoplasm


What is the cell cycle? The

The process that all body cells in multicellular organisms use to grow and divide


What are the chromosomes made of when mitosis begins?

Two strands joined in the middle by a centromere. The separate strands are called chromatids


Why are there two strands?

Each chromosome has already made an indentical copy of itself during interphase. When mitosis is over, chromatids, end up as one-strand chromosome in the new daughter cells


Describe metaphase

Chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.


What happens at the metaphase checkpoint

The cell checks that all the chromosomes are attached to the spindle before mitosis can continue


Anaphase describe

Centromeres divide separating each pair of sister chromatids. The spindle contracts, pulling chromatids to opposite ends of the cell, centromere first.



Chromatids reach opposite poles in the spindle. They uncoil and become long and thin again. Called chromosomes again. Nuclear envelope forms around each group of chromosomes so there are two nuclei



Cytoplasm divides in animal cells a cleavage furrow forms to divide the cell membrane. There are now two daughter cells that are genetically identical to the original cell to each other. Cytokinesis usually begins in anaphase and ends in telophase.
Separate process to mitosis


How can you observe the cell cycle?

Stain chromosomes
So you can see under microscope meaning you can watch what happens during mitosis.


How do you recognise cells in interphase?

The chromosomes will be spread out and not condensed


Meiosis produces what?

Gametes for sexual reproduction


What happens in sexual reproduction?

Two gametes join together at fertilisation to form a zygote. Zygote then divides and develops into a new organisms


What type of cell division is meiosis?

One that happens in the reproductive organs to produce gametes


What does meiosis involve?

A reduction division
Cells that divide by mitosis produce full number of chromosomes to start with but cells that are found that are formed from meiosis have half the number.
Cells with half the normal number of chromosomes (haploid cells)


What are cells formed by meiosis?

Genetically different because each new cell ends up with a different combination of chromosomes


Why is meiosis so important?

Without meiosis, the number of chromosomes double when the gametes fused.


What does mitosis involve in terms of divisions?

Meiosis 1 and meiosis 2


What is meiosis 1?

A reduction division


What are meiosis I and meiosis II split up into?



What does meiosis begin with?

During interphase, DNA unraveled and replicates to produce double-armed chromosomes called sister chromatids


Prophase I

Chromosomes condense getting shorter and fatter
Chromosomes arrange themselves into homologous pairs and crossing-over occurs. Like in mitosis, centrioles start moving to opposite ends of the cell forming the spindle fibres. Nuclear envelope breaks down


Metaphase I

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


Anaphase I?

Spindles contract separating homologous pairs- one chromosomes goes to each end of the cell


Telophase I?

Nuclear envelope forms around each group of chromosomes



Division of cytoplasm occurs and two haploid daughter cells are produced


Humans chromosome number?

46 chromosomes
23 pairs


Where did the two chromosomes come from?

One chromosome in each pair came from mum and one from dad.


What are the chromosomes that make up each pair?

Same size
Same genes (can be different alleles)
Called homologous pairs


What happens after Meiosis I?

Meiosis II
Two daughter cells undergo prophase II, metaphase II, anaphase II, telophase II, cytokinesis (a lot like mitosis)


Anaphase II?

Pairs of sister chromatids are separated each new daughter cell inherits one chromatid from each chromosome. Four genetically different haploid daughter cells are produced. These are gametes


When does chromosome cross over in meiosis happen?

During prophase I of meiosis I, homologous pairs of chromosomes vine together and pair up. Chromatids twist around each other and bits of chromatids swap over. The chromatids still contain the same genes but now have different combinations of alleles


Two main events leading to genetic diversity?

Crossing over of chromatids
Independent assortment of chromosomes


Crossing over of chromatids

Happens in meiosis I
Means each of the four daughter cells formed from meiosis contain chromatids with different alleles


What is each homologous pair of chromosomes in your cell made of?

One chromosome from maternal and one chromosome from paternal


When do homologous pairs line up?

Metaphase I


When do homologous pairs separate?

Anaphase I


What happens as a result of this?

It's completely random which chromosome from each pair ends up in which daughter cell


What do the four daughter cells produced by meiosis have?

Completely different combinations of those maternal and paternal chromosomes


What is this process called?

Independent assortment of the chromosomes


What does this shuffling of chromosomes lead to?

Genetic variation in any potential offspring


What are multicellular organisms made of?

Many different cell types that are specialised for their function e.g. Liver cells, muscle cells, white blood cells


What did all these specialised cell types originally come from?

Stem cells


Stem cells are?

Unspecialised cells
Can develop into different types of cells


Who has some sort of form of stem cells?

All multicellular organisms


When are stem cells found in humans?

Early embryos and in a few places in adults.
Stem cells in early embryos can develop into any type of human cell. Adult stem cells can only develop into a limited range of cells


How do stem cells specialise?

Divide to form new cells via Differentation


What are adult stems cell used for in animals?

Replace damaged cells e.g. Make new skin or blood cells


What are stem cells needed for in plants?

To make new shoots and roots throughout their stem cells because they are always growing


What can stem cells in plants differentiate?

Various plant tissues including xylem and phloem


What else can a stem cell do?

Divide to produce more undifferentiated stem cells e.g. Can renew themselves


What do cells in the bone marrow do?

Differentate into blood cells


What are bones?

Living organs containing nerves and blood vessels main bones of the body have narrow in the centres


What do adult stem cell do here?

Divide and differentiated to replace worn out erythrocytes and neutrophils


Cell in meristem

Stem cells found in meristem
In root and stem cells of vascular cambium divide and differentiate to become xylem and phloem sieve tubes


What could stem cells be used for?

Replace damaged tissue in a range of conditions e.g. Might be possible to use stem cells to treat neurological disorders like Alzheimer's and Parkinson's


How can stem cells help Alzheimer's?

Nerve cells in the brain die in increasing numbers resulting in severe memory loss. Researchers are hoping to use stem cells to regrow healthy nerve cells in people with Alzheimer's


How can stem cells treat Parkinson's?

Suffer from tremors that they can't control. The disease causes the loss of a particular nerve cell found in the brain needed to control movement. Transplanted stem cells may help regenerate the dopamine-producing cells


What else can stem cells be used for?

By scientists researching developmental biology how organism grow and develop
Studying stem cells can help us to understand more about things like developmental disorders and cancer


What happens when cells differentiate?

They have a specific function
Structure is adapted to perform that function


Describe neutrophil

Type of white blood cells
Defends body against disease
Flexible shape allows them to engulf foreign particles or pathogens. Many lyposijes in their cytoplasm contain digestive enzymes to break down engulfed particles



Carry oxygen in blood
Biconcave disc shape provides a large surface area for gas exchange. Have no nucleus so more room for haemoglobin


Epithelial cells

Cover surface of organs
Cells joined by interlinking cell membranes and a membrane at their base. Ciliated epithelia have cilia that beat to move particles away. Squamous epithelia are very thin to allow efficient diffusion of gases


Sperm cell

Flagellum so can swim to egg
Have microchrondria to provide energy to swim
Acrosome contains digestive enzymes to enable sketch to penetrate surface of egg


Palisade mesophyll cell

In leaves
Do most of photosynthesis
Contain many chloroplasts so absorb a lot of sunlight.
Thin walls so carbon dioxide can easily diffuse into the cell.


Root hair cell

Absorb water and minerals ions from soil
Large surface area for absorption and a thin permeable cell wall for entry for water and ions. The cytoplasm contains extra mitochondria to provide the energy needed for active transport


Guard cells

Found in pairs with a gap between them to form a stoma
One of the tiny pores in the surface of the leaf used for gas exchange
In light, guard cells take up water and become turgid
Thin outer walls and thickened inner walls force them to bend outwards opening the stoma allowing leaf to exchange gases for photosynthesis


What's a tissue?

A group of cells plus ant extracellular material secreted by them that are specialised to work together to carry out a particular function. A tissue can contain more than one type of cell


Squamous epithelium

Single layer of flat cells lining a surface
Found in many places including alveoli in the lungs


Ciliated epithelium

Layer of cells covered in cilia
Found on surface where things need to be moved
In the trachea for instance where cilia waft mucus along


Muscle tissue

Made up of bundles of elongated cells called muscle fibres
Three different types of muscle tissue: smooth (found lining the stomach wall), cardiac (found in the heart), skeletal (used to move) all slightly different in structure



Type of connective tissue found in the joints
Shapes and supports the ears, nose and windpipe
Formed when cells called chondroblasts secrete an extracellular matrix (jelly-like substance containing protein fibres) which become trapped inside


Xylem tissue

Transports water around plant
Supports plant
Contains hollow xylem vessel cells which are dead and living parenchyma cells
Perforated by pits
Parenchyma cell fills in gaps between vessels


Phloem tissue

Transport sugars around plant
Arranged in tubes
Made of sieve cells, companion cells and some ordinary plant cells


Sieve cell

Has end walls with holes in so sap can move easily through them. End walls called sieve plates



Group of different tissues that with together to perform a particular function



Contain squamous epithelial tissue in the alveoli
Ciliated epithelial tissue in the bronchi
Have elastic connective tissue and vascular tissue in the blood vessels



Contain palisade tissue for photosynthesis as well as epidermal tissue to prevent loss from the leaf
Xylem and phloem tissues in the veins


What do organs work to form?

Organ systems- each system had particular function


Respiratory system

Made of all organs, tissue and cells involved in breathing
Lungs, trachea, larynx, nose, mouth and diaphragm are all part of the respiratory system


Circulatory system

Made up of organs involved in blood supply
Heart, arteries, veins and capillaries