2.6- Cell division, cell diversity and cellular organisation Flashcards
What is the cell cycle?
The process that all body cells in multicellular organisms use to grow and divide
What are the two periods in the cell cycle called?
Interphase and M Phase (M phase involves mitosis and cytokinesis)
What occurs in interphase?
Cell growth and DNA replication
What occurs in M phase?
Mitosis and cytokinesis
What are the three growth stages of interphase?
G1,S,G2
What occurs during G1?
Cell grows and new organelles and proteins are made
What occurs during the synthesis phase?
Cells replicate DNA ready to divide by mitosis
What occurs during G2?
Cell keeps growing and proteins needed for cell division are made
What occurs at the G1 checkpoint?
That cell checks that the chemicals needed for replication are present and for any damage to the DNA (this occurs before entering S phase)
What occurs at the G2 checkpoint?
The cell checks whether all the DNA has been replicated without any damage. If it has the cell can enter mitosis.
What are the four stages of mitosis?
Prophase, metaphase, anaphase, telophone,
What occurs during prophase?
- The chromosomes condense, getting shorter and fatter.
- Centrioles start moving towards opposite ends of the cell
- The nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What occurs during metaphase?
What occurs during metaphase?
What occurs during anaphase?
- The centromeres Divide separating each pair of chromatids
- The spindles contract pulling chromatids towards opposite ends of the cell
What occurs during telophase?
- The chromatids reach the opposite poles of the spindle and 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 new nuclei
What is cytokinesis?
Where the 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 each other.
Cytokinesis is a separate process to mitosis
What occurs during interphase?
- The cell carries out normal functions but also prepared to divide
- The cells DNA is unravelled and replicated to double its genetic content
- The organelles are also replicated so it has spare ones and it’s ATP content is increased
How can you observe the cell cycle and mitosis?
You can stain chromosomes (using Giemsa stain) so that you can see them under a microscope and watch what happens during mitosis.
What does meiosis produce?
Gametes for sexual reproduction
Why are cells produced in meiosis genetically different to each other?
Each new cell ends up with a different combination of chromosomes
What are haploid cells?
Cells with half the normal number of chromosomes
How many divisions in meiosis?
2, meiosis I and meiosis II
What happens in prophase 1?
The chromosomes condense
The chromosomes and arrange themselves into homologous has and crossing over occurs
Centrioles style after the ends of the cell
The nuclear envelope breaks down
What happens in metaphase 1?
The homologous pairs line up across the centre of the cell and attach to spindle fibres
What happens in anaphase 1?
The spindles contracts, separating the homologous pairs
What happens in telophase 1?
A nuclear envelope forms around each group of chromosomes
What happens in prophase 2?
The chromosomes condense
The chromosomes and arrange themselves into homologous has and crossing over occurs
Centrioles style after the ends of the cell
The nuclear envelope breaks down
What happens in metaphase 2?
The homologous pairs line up across the centre of the cell and attach to spindle fibres
What happens in anaphase 2?
The pairs of sister chromatids are separated and each new daughter cell inherits one chromatid from each chromosome
Four genetically different daughter cells are produced(gametes)
What is the overall aim of meiosis?
The half the chromosome number(reduction division)- this occurs during meiosis 1
How does chromatids crossing over cause variation in meiosis?
During prophase 1, chromatids twist around each other and bits of chromatids swap over
The chromatids still contain the same genes but now have a different combination of Alleles
How does meiosis produce cells which are genetically different? (2 ways)
Crossing over of chromatids
Independent assortment of chromosomes
How does the independent assortment of chromosomes produce genetic variation?
When the homologous pairs line-up in metaphase 1 and are separated in anaphase 1, they pair up completely randomly
This leads to genetic variation
What are stem cells?
Unspecialised cells that can develop into different types of cells
Where is stem cells found in humans?
Early embryos - can develop into any type of human cell
Adults- can develop into a limited range of cells
What is differentiation?
The process by which a cell becomes specialised for its job
How are stem cells used in adults?
To replace damaged cells for skin or blood cell
How are stem cells used in plants?
To make new shoots and roots throughout their lives as the plant grows
How are blood cells created?
Adult stem cells in the bone marrow divide and differentiate to replace worn-out blood cells
How could stem cells be used to treat Alzheimer’s?
Stem cells could help regrow nerve cells for people with Alzheimer’s
How could stem cells be used to treat Parkinson’s?
Transplanted stem cells to regenerate the dopamine producing cells
How are neutrophils specialised?
The flexible shape allows them to engulf foreign pathogens
The many lysosomes in the cytoplasm contain digestive enzymes to break down in golf particles
They have a lobed nucleus to squeeze through small capillaries
How are erythrocytes specialised?
The biconcave disc shape provides a large surface area for gas exchange
They have no nucleus so there’s more room for haemoglobin
How are epithelial cells specialised?
Ciliated epithelium of cilia that move particles away
Squamous epithelium in the lungs are very thin to allow efficient diffusion of gases
How are sperm cells specialised?
They have a flagellum so they can swim to the egg
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 cells specialised?
They contain many chloroplasts so they absorb a lot of sunlight
The walls are thin so carbon dioxide can easily diffuse in the cell
How are root hair cells specialised?
They have a large surface area for absorption
They have a thin permeable cell wall for entry of water and ions
The cytoplasm contains extra mitochondria to provide energy for active transport
How are guard cells specialised?
Guard cells are found in pairs with a gap between them to form a stoma
In the light, guard cells take up water and become turgid, forcing them to bend outwards allowing gas exchange for photosynthesis
They also stop water loss during the night
What is a tissue?
A group of cells that are specialised to work together to carry out a particular function
What are four examples of animal tissue?
Squamous epithelium
Ciliated epithelium
Muscle tissue
Cartilage
What are two examples of plant tissue?
Xylem tissue
Phloem tissue
What is an organ?
A group of different tissues that work together to perform a particular function
What are two examples of organs?
The lungs
Leaves
What is an organ system?
A group of organs working together to perform a particular function
What are two examples of organ systems?
The respiratory system
The circulatory system
What is squamous epithelium?
A single layer of flat cells lining a surface
It is found in many places, including the alveoli in the lung
What is ciliated epithelium?
A layer of cells covered in cilia
It’s found on surfaces where things need to be moved
Example: Trachea
What is the role of xylem tissue?
It transports water around the plant and it supports the plant
What is the role of phloem tissue?
It transports sugars around the plant
It’s arranged into sand is made up of sieve tubes, companion cells and some ordinary plant cells
