Cell division, Cell diversity and Cell differentiation part 2 Flashcards
1
Q
Why do Multicellular organisms need differentiation
A
- In multicellular organisms specialised cells are needed to carry out specific functions, as most of their cells are not in direct contact with the external environment therefore they are needed to carry out functions
2
Q
Why do single celled organisms not need differentiation
A
- In single celled organisms each organelle has a specific function, and they are in contact with the external environment this means that they are small and have a large surface area to volume ratio so that oxygen can disuse across their plasma membrane and waste products can diffuse out of the same membrane
3
Q
How do differentiated cells form
A
- Multicellular eukaryotic organisms start a life as a single undifferentiated cell called a zygote
- Zygote – this results from when an ovum is fertilised by a spermatozoon and two haploid nuclei fuse to give a cell with a diploid nucleus
- Zygote is not specialised and all the genes in the genome are expressed, it is able to divide by mitosis as it is a stem cell, after several mitosis divisions an embryo forms containing many undifferentiated embryonic stem cells
- Embryonic stem cells differentiate as certain genes are switched off and others expressed
4
Q
embryonic cells differentiate as certain genes are switched off and other genes are expressed more this is so that
A
- the proportions of the different organelles differ from those of other cells
- the shape of the cell changes
- some contents of the cell change
5
Q
What do erythrocytes do
A
carry oxygen from the lungs to respiring tissue
6
Q
How are erythrocytes specialised
A
- They are small so therefore have a large surface area to volume ratio this means that lots of oxygen can diffuse into the cell and easily reach all regions
- Flexible so have a well-developed cytoskeleton this allows the erythrocytes to change shape so they can twist and turn as they travel through narrow capillaries
- Most organelles are lost a differentiation – have no nucleus, mitochondria or ER, and little cytoplasm – therefore they can have a large amount of haemoglobin
- Haemoglobin is synthesised within immature erythrocytes while they still have a nucleus, ribosomes and endoplasmic reticulum
7
Q
What do neutrophils do
A
ingest invading pathogens
8
Q
How are neutrophils specialised
A
- Twice the size of erythrocytes
- Contain a multilobed nucleus
- Attracted to and travel towards infection sites by chemotaxis
- Function is to ingest bacteria and some fungi by phagocytosis
9
Q
How are spermatozoa specialised
A
- Many mitochondria to carry out aerobic respiration allowing the undulipodium to move and propel the cell towards the ovum
- Spermatozoa are small, long and thin so they can move easily
- Once it reaches an ovum enzymes are released from the acrosome these digest the outer protective layer which covers the ovum and allows the sperm head to enter the ovum
- Head contains haploid male gamete nucleus and very little cytoplasm
10
Q
How are epithelia cells specialised
A
- Squamous epithelial cells are flattened in shape in order to increase surface area
- Many of the cells have cilia
11
Q
How are palisade cells specialised
A
- Long an cylindrical – therefore they are closely packed but they have space between them so that the air can circulate and carbon dioxide can diffuse into cells
- Large vacuole so that chloroplasts are near to the periphery of the cell this reduces the diffusion distance for carbon dioxide
- Contain chloroplasts
- Contain cytoskeleton threads and motor proteins, these move the chloroplasts nearer to the upper surface of the leaf when there is low sunlight intensity but down the leaf when there is high sunlight intensity
12
Q
How are guard cells specialised
A
- Light energy used to produce ATP
- ATP transports potassium ions from surrounding epidermal cells into the guard cells by active transport and lowers the water potential
- Water enters the guard cells from neighbouring epidermal cells by osmosis
- Guard cells swell but at tips the cellulose cell wall is more flexible and is more rigid when it is thicker the tips bulge and the gap between them enlarges
- As the stomata open air can enter the spaces within the layer of cells beneath the palisade cells
- Gaseous exchange occurs and carbon dioxide will diffuse into the palisade cells – they use this for photosynthesis and this will maintain a steep concentration gradient
- Oxygen produced during photosynthesis can diffuse out of the palisade cells into the air spaces and out through open stomata
13
Q
How are root hair cells specialised
A
- Hair like projection increases surface area for absorption of important things such as water and mineral ions as well as nitrates
- Mineral ions are actively transported lowering the water potential then causing the water to follow into them by osmosis down the water potential gradient
- Root hair cells have special carrier proteins in the plasma membrane carry out active transport
- The cells ATP which is needed for active transport
14
Q
What are the four main tissue types
A
- epithelial
- connective tissue
- muscle tissue
- nervous tissue
15
Q
What is the role of connective tissue
A
hold structures together and provide support
16
Q
what is the role of muscle tissue
A
made out of cells that are specialised to contract and cause movement
17
Q
what is the role of nervous tissue
A
made of cells specialised to conduct electrical impulses
18
Q
what is the role of epithelial tissue
A
lining tissue
19
Q
what is tissue
A
a groups of cells that work together to perform a specific function
20
Q
How is epithelial tissue specialised
A
- Covers surfaces of the body
- Cells are close together and form continuous sheets
- No blood vessels, but they receive nutrients by diffusion from tissue fluid in the underlying connective tissue
- Have smooth surfaces but some have cilia or microvilli
- Have short cell cycles and divide up to two or three times a day to replace worn or damaged tissue
- Functions – protection, absorption, filtration, excretion, and secretion
21
Q
How is connective tissue specialised
A
- Widely distributed in the body. Consists of non-living extracellular matrix containing proteins and polysaccharides which separates the living cells within the tissues and enables it to withstand weight
22
Q
How is cartilage cells specialised
A
- Immature cells in cartilage are called chondroblasts, they divide by mitosis and secrete the extracellular matrix. Once the matrix has been synthesised the chrondroblasts have become mature, less active chondrocytes maintain the matrix.
