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
What does heterozygous mean?
An individual with two different alleles present
What is a phenotype?
The physical characteristics of an organism
What does dominant mean?
An allele that always shows it’s effect as a phenotype and masks the presence of the other form
What does recessive mean?
An allele that is masked by the dominant allele
What is an organisms genotype?
The set of genes (alleles) possessed by an individual
what does the medulla do?
Controls heart rate and breathing rate
what does the cerebellum do?
Controls balance and coordination
What does the cerebrum do?
Responsible for conscious thoughts, reasoning, memory and emotions
3 main parts of the mammalian circulatory system?
the blood
the heart
the blood vessels
what does blood do?
It transports nutrients and oxygen to respiring cells. It also transports carbon dioxide from respiring cells to lungs
name 3 features of the red blood cell that help if it completes its job of transporting oxygen around the body
Biconcave shape provides a larger surface area to more oxygen
No nucleus allows more haemoglobin to be present
Haemoglobin attaches to oxygen
what do white blood cells do?
white blood cells are part of the immune system and are involved in destroying pathogens (disease causing micro-organisms) emg bacteria.
what are the two types of white blood cells?
phagocytes
lymphoctyes
what do phagocytes do?
Phagocytes carry out phagocytosis by engulfing and digesting pathogens
what are lymphocytes?
some lymphocytes produce antibodies which destroy pathogens. Each antibody is specific to a particular pathogen
how many valves are there in the heart?
4
what is the purpose of valves?
they prevent the backflow of blood
where does blood from all over the body enter the heart?
is the blood oxygenated or deoxygenated?
the right atrium of the heart in a vein known as the vena cava
the blood is deoxygenated
where does the blood go after it enters the body in the right atrium?
from there blood is then pumped into the right ventricle,through a valve and then away from the heart in the pulmonary artery.
what does the pulmonary artery do?
It carries deoxygenated blood to the right and left lung so that it can pick up oxygen
after the blood has left the heart through the pulmonary artery what happens?
The oxygenated blood returns to the left atrium in the pulmonary vein. Blood then flows from the left atrium, through a valve to the left ventricle and leaves the heart in the aorta
how does the heart get its own supply of blood?
Through the coronary arteries
how can a heart attack occur?
if the coronary arteries become blocked or narrowed in any way then a heart attack can occur
where do coronary arteries come from?
they branch off from the aorta
what are the three types of blood vessels and their purpose.
arteries - carry blood away from the heart
capillaries are involved in the exchange of materials emg carbon dioxide and oxygen
veins carry blood to the heart
what do arteries do?
3 features of arteries
arteries carry blood away from the heart.
arteries :
have thick, muscular walls
have a narrow central channel
carry blood under high pressure away from the heart
do arteries carry oxygenated or deoxygenated blood around the body?
arteries carry oxygenated blood
identify 3 features of a capillary network
has a large surface area
in close contact with tissue cells
have thin walls (one cell thick)
what do veins do?
identify 4 features of a vein
veins carry blood towards the heart.
veins:
have thinner walls
a wider channel
carry blood under low pressure towards the heart
contain valves
