Biology: Stem Cells and Specialised Cells

a type of cell that can differentiate into many different types of cells

they are unspecialised and so are not adapted to any particular function

tissues not efficiently replaced leading to aging

can form tumours which can lead to the development of cancer

a stem cell’s ability to differentiate into different cell types

stem cells that can differentiate into any type of cell

stem cells that can form any tissue type but not whole organisms

stem cells that can only form a range of cells within a certain type of tissue

groups of cells working together as one unit can make use of resources more efficiently than single cells

they look very different to other cells as they are adapted to their function, white blood cells can fight off pathogens and at the same time red blood cells can supply oxygen to respiring tissues

they have a short life span of around 120 days so need to be replaced consistently, located in the bone marrow

they live about 6 hours and stem cells produce around 1.6 billion per kg per hour

embryonic stem cells and tissue (adult) stem cells

embryonic- totipotent but pluripotent once blastocyst (mass of cells) is formed after a few days

tissue- multipotent

embryonic- early stage of embryo development

tissue- bone marrow or umbilical cord

in the meristem tissue which is found where growth is occurring e.g., tips of roots and shoots

pluripotent

vascular cambium, growth of plant as the vascular tissue grows as the plant grows, form xylem and phloem cells

heart disease, type 1 diabetes, parkinsons, alzheimers, birth defects, spinal injuries

burns- new skin can be grown from stem cells

new drugs can be tested on cultures of stem cells rather before animals

they can be used to study the changes as multicellular organisms grow

religious and moral belief that life starts at conception and so when the cell is destructed during harvesting it is murder, rights of ownership

only multipotent cells which restricts their usefulness

1. very small, have large SA to V ratio increased by the biconcave shape means oxygen can easily diffuse across their membranes

2. flexible due to well developed cytoskeleton, allows them to change shape so they can twist and turn as they travel through very narrow capillaries

3. most organelles lost at differentiation provides more space for haemoglobin molecules

1. many mitochondria to provide lots of ATP for the tail to move and propel the cell

2. small but long and thin so they can move easily

3. has an acrosome (special type of lysosome) which releases enzymes to digest outer covering of ovum

1. flexible shape which can mold to the shape of its target

2. twice the size of erythrocytes so they can ingest pathogens

1. many have cilia which are used to waft substances in one direction

2. squamous epithelial cells are flattened in shape and form a thin cross-section which shortens the diffusion pathway and is permeable

1. long and cylindrical, pack together quite closely with little space between them for air to circulate, co2 in the air spaces diffuse into cells

2. large vacuole so that chloroplasts are positioned near the periphery of the cell reducing diffusion distance for co2

3. contain many chloroplasts for photosynthesis

4. contain cytoskeleton threads and motor proteins to move the chloroplasts up or down the leaf depending on light intensity

1. they use light energy to produce ATP in order to actively transport potassium ions from the surrounding epidermal cells into the guard cells, lowering their water potential

2. when water enters via osmosis they swell causing the stomata to enlarge, they are now open and gaseous exchange can occur so co2 can enter the palisade cells for photosynthesis

3. oxygen can also diffuse out when stomata are open, when the plant doesnt want anything to diffuse out the guard cells lose water and become flaccid closing the stomata

1. hair like projection increases surface area for absorption of water and mineral ions from the soil into which it projects

2. special carrier proteins in the plasma membranes in order to actively transport mineral ions in

3. produce ATP required for active transport

4. as the mineral ions actively transport in, it lowers the water potential allowing water to enter via osmosis

1. consists of flattened cells which form a protective covering over leaves, stems and roots

2. some have walls impregnated with a waxy substance forming a cuticle to prevent water loss from the plant

1. xylem vessels carry water and minerals from roots to all parts of the plant

2. phloem sieve tubes transfer products of photosynthesis from leaves to other parts of the plant that don’t photosynthesise

1. can divide by mitosis and differentiate into other types of cells

1. lignin is deposited into the meristematic cells cell walls to reinforce and water proof them, this does kill them

2. the ends of the cell breaks down so that the xylem forms continuous columns with wide lumens to carry water and dissolved minerals

1. sieve tubes lose most of their organelles and sieve plates develop between them

1. companion cells retain their organelles and continue metabolic functions to provide ATP for active loading of sugars into the sieve tubes

1. have short cell cycles so can divide up to 2 or 3 times a day to replace worn or damaged tissue

2. no blood vessels receive nutrients via diffusion so have a very thin cross section to shorten diffusion pathway

1. the matrix within the cells separates the living cells within the tissue enabling it to withstand forces such as weight

1. muscle cells are called fibres that are elongated and contain special organelles called myofilaments which allow the muscle tissue to contract