multicellular organisms Flashcards
what is mitosis
mitosis is the process by which the nucleus divides into two daughter nuclei, each of which receives exactly the same number of chromosomes as were present in the original nucleus. This is then followed by division of the cytoplasm to produce two identical daughter cells.
what is the sequence of events during cell division / mitosis
- chromosomes replicate to become thicker visible pairs or chromatids
- the chromosomes line up along the equator of the cell, attached to spindle fibres.
- Their pairs of chromatids are pulled apart by spindle fibres to opposite poles of the cell.
- Two new nuclei form around the chromatids which are now called chromosomes
- After mitosis the cell cytoplasm becomes pinched off and two genetically identical daughter cells are formed.
how many sets of chromosomes do sex cells have?
a sex cell (gamete) has one set of chromosomes and is described as haploid (23)
how many sets of chromosomes do non sex cells have?
Non sex cells have two sets of chromosomes and are described as diploid (46)
identify two cell types and explain a feature it has and it’s function
red blood cell:
features - biconcave shape, relatively large surface area, contains haemoglobin
function - to transport oxygen around the body.
sperm:
feature - has a tail & a large number of mitochondria
function - to swim to and fertilise egg
identify two plant cells types and explain a feature it has and it’s function
xylem vessel:
feature - hollow tube; wall strengthened by lignin; lignin deposited as rings or spirals allowing expansion and contraction
function - support and water transport up the plant
spongy mesophyll:
feature - round shape allows loose arrangement in contact with moist air spaces for absorption of carbon dioxide
function - secondary region of photosynthesis
describe the two types of stem cells
embryonic stem cells
stem cells can be obtained from the embryo at a very early stage, they have the potential to become any cell type found in the body
tissue stem cells
tissue stem cells can be found in the body throughout life. They have the potential to become only a few types of cells
what is the function of the xylem
transports water and minerals from soil to leaf
what is the function of the phloem?
Transports sugars made during photosynthesis to the rest of the plant
where in the plant does photosynthesis take place?
The palisade mesophyll cells
what does the upper epidermis do?
protects the leaf and allows light to pass through the layer below
What does the stoma do?
Allows carbon dioxide to enter the leaf and oxygen to exit the leaf
what is the function of the guard cells?
Controls gas exchange between the leaf and the air outside.
why are root hair cells specialised to have a large surface area?
to absorb water from the surrounding soil
What is the process by which water moves up the plant and is lost by evaporation from stomata in the plant leaves called?
Transpiration
what is a gene?
A region of DNA on a chromosome that codes for a particular characteristic
what is an allele?
Different forms of the same gene
What does homozygous mean?
An individual with two copies of the same allele present