Cells and Control Flashcards
What are rods and cones
The light sensitive cells in the retina
How do rods and cones differ?
Rods detect in dim light but only black and white. Cones don’t work in dim light but detect colour
What does the cornea do?
Refracts light
Explain refraction
As the light wave moves from matter with different density it bends
What is the pupil
The hole made by the iris which controls how much light enters the retina
What does the lens do?
Refracts light
How does the lens work?
It changes shape to focus the light onto the retina.
To look at distant objects the ciliary muscle relaxes and the suspensory ligaments pull tight which elongates the lens.
To look at near objects the ciliary muscle contracts and the suspensory ligaments relax so the lens becomes more rounded.
What is the conjunctiva
Protective membrane at front of eye
What is a cataract
A cloudy patch on the lens which stops light being able to enter the eye and causes blurred vision
What is colour blindness
People can’t differentiate colours due to defects in the cone cells, most commonly red/green
Where does the image fall in the eye in long sightedness
Behind the retina
Where does the image fall in the eye in short sightedness
In front of the retina
What is a concave lens?
One that is hollowed out each side - like a cave
https://www.bbc.co.uk/bitesize/guides/zt7srwx/revision/1
What is a convex lens
One that is rounded each side
What is long sightedness?
Can’t focus on near objects. The eyeball is too short or the lens the wrong shape and doesn;t bend the light enough. The image falls behind the retina.
What is short sightedness
Can’t focus on far objects. The eyeball is too long or the lens the wrong shape and bends the light too much. The image falls in front of the retina.
What is the retina
The light sensitive part of the eye
What is the nerve for the eye called
Optic nerve
What does the optic nerve do?
Light falling on the rods and cones causes electrical impulses to be created which the optic nerve carries to the brain.
What is a chromosome
Coiled up lengths of DNA molecules which form the genetic material found in the cell nucleus
What chromosomes does a body cell have?
23 pairs of chromosomes altogether with two copies of each (total 46) one copy from the father and one from the mother
How do cells divide?
Mitosis
What is mitosis
The part of the cell cycle called cell division where one cell divides to form two identical daughter cells
Why is cell divsion needed
For growth and repair of damaged cells.
It also enables asexual reproduction.
What is the cell cycle
The cell cycle consists of the interphase and mitosis and cytokinesis
What is the Interphase
In a non dividing cell DNA is spread in long strings. Before divsion the cell has to grow and increase the numbers of subcellular structures eg ribosomes/mitochondria. It then duplicates it’s DNA so there is a copy for each new cell. The chrmosomes go from being shaped like I to X.
What are the four stages of mitosis?
PMAT
Prophase
Metaphase
Anaphase
Telophase
What happens in prophase
Chromosomes condense, membrane around nucleus breaks down, chromosomes lie free in cytoplasm
What happens in metaphase
Chromosomes line up in centre of cell
What happens in anaphase
Spindle fibres pull chromosomes apart. The chromatids are pulled to opposite ends of cell.
What happens in telophase
Membranes form around each set of chromosomes and these become the nuclei of the two new cells - the nucleus has divided.
What is cytokinesis
The process at the end of the telophase when the cytoplasm and cell membrane divide to form two separate cells
How can you calculate the number of cells after multiple divisions by mitosis
Use the formula 2 to power n
n is the number of divisions
What is growth
An increase in size or mass
What are the processes of growth?
cell division, differentiation and elongation
What is cell differentiation
Process of cell changing to be specialised for it’s job.
Why do we need specialised cells
It helps multicellular organisms be more efficient
What is cell elongation
Process where a plant cell expands making it bigger so the plant grows
How do animals grow
All growth by cell division. Most growth when young so cells divide at fast rate then stop and cell division is just for repair. Downside is cell differentiation is lost at an early stage
How do plant cells grow
Height is mainly from cell elongation. Cell division just in roots and shoots.
Plants grow continuously even old trees can produce new parts so continue to differentiate
What is cancer
uncontrolled cell division
How does cancer occur
The rate of mitosis is controlled by chemical instructions from genes in an organisms DNA. If there is a change in one of the genes that controls cell division the cell might start dividing uncontrollably. This results in a mass of abnormal cells - a tumour. If the tumour invades and destroys surrounding tissue it is called cancer.
How is growth monitored
with percentile charts
Why are growth charts used
to assess child’s growth over time so an overall pattern of development can be seen and problmes highlgted eg dwarfism, malnutrition, obesity
What measurements are taken regularly of babies?
length, mass and head circumference
What is a percentile chart
It shows a number of percentiles eg 50% percentile is what 50% of babies will have achieved at that age.
What percentiles are investigated
top, bottom two and any sudden change from one to another or falling away from a percentile
What is a stem cell
An undifferentiated cell that can differentiate into different types of specialised cell.
Depending on what instructions they are given stem cells divide by mitosis to become new cells then differentiate
Where are stem cells found in
Animals:
early human embryos
bone marrow
Plants:
Meristem roots and tips
Why are stem cells important
They are important for the growth and development of organisms
What are embryonic stem cells
cells which have the potential to divide and produce any type of cell
What can adult stem cells do
They can only produce certain cells only certain ones like blood cells
What is the meristem
The part of the plant where cell division occurs which is in th eparts of the plant which is growing eg roots and shoots.
They produce unspecialised cells that can divide to form any cell type like embryonic stem cells but they last as long as the plant lives
Give examples of specialised plant cells
Xylem, Phloem
How are stem cells used in medicine
Adult stem cells are used to cure diseases eg bone marrow transplant for sickle cell
Embryonic stem cells can be extracted to grow certain speicalised cells
Potential to create specialise cells to replace damaged cells eg cardiac muscle transplanted into someone with heart disease
What are the risks of using stem cells?
Tumour development if cell division isn;t controlled may get a tumour
Disease tranmission from viruses living inside cells
Rejection if transplanted cells are not the patients own body reacts as thought they are foreign and mounts an immune response to try and get rid of them. Patient can take drugs to suppress the reponse but this makes them susceptible to disease.
There are also ethical issues
What does the nervous system do?
Lets you react to what is aorund you
