Bio Questions Flashcards
Explain the function of heart
Deoxygenated blood coming from the body flows into the right atrium via the vena cava
Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle
The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart
The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure)
Oxygen-rich blood returns to the left atrium via the pulmonary vein
It passes through the bicuspid (atrioventricular) valve into the left ventricle
The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body
The semilunar valve in the aorta prevents the blood flowing back down into the heart
Explain the uptake of xylem
Water molecules are attracted to each other by cohesion - creating a continuous column of water up the plant
Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem
Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves
As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant
If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker
Explain the structure of arteries
Arteries
Have thick muscular walls containing elastic fibres to withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through
Have a narrow lumen to maintain high pressure
Explain the structure of veins
Veins
Have a large lumen as blood pressure is low
Contain valves to prevent the backflow of blood as it is under low pressure
Explain the structure of capillaries
Capillaries
Have walls that are one cell thick so that substances can easily diffuse in and out of them
Have ‘leaky’ walls so that blood plasma can leak out and form tissue fluid surrounding cells
Explain thr structure of arterioles and venules
Arterioles and venules
As arteries divide more as they get further away from the heart, they get narrower
The narrow vessels that connect arteries to capillaries are called arterioles
Veins also get narrower the further away they are from the heart
The narrow vessels that connect capillaries to veins are called venules
How does Vibrio cholerae cause diarrhoea?
Bacteria attach to the wall of the small intestine
They produce a toxin
The toxin stimulates the cells lining the intestine to release chloride ions from inside the cells into the lumen of the intestine
The chloride ions accumulate in the lumen of the small intestine and lower the water potential there
Once the water potential is lower than that of the cells lining the intestine, water starts to move out of the cells into the intestine (by osmosis)
Large quantities of water are lost from the body in watery faeces
The blood contains too little chloride ions and water
Explain the process of ultrafiltration
Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup-shaped Bowman’s capsule
The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta)
This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate
This process is known as ultrafiltration
The substances forced out of the capillaries are: glucose, water, urea, salts
Some of these are useful and will be reabsorbed back into the blood further down the nephron
Explain selective reabsorption
After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule
This takes place by active transport
The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules
Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule
Explain the process of fertilisation in plants
Fertilisation occurs when a pollen nucleus fuses with an ovum nucleus in the ovule
As the pollen has no ‘tail’ to swim to the ovary of a plant, in order to reach the ‘female’ nucleus in the ovary it has to grow a pollen tube
This only happens if the pollen grain has landed on the right kind of stigma (i.e. of the same species as the flower the pollen came from)
The nucleus inside the pollen grain slips down the tube as it grows down the style towards the ovary
The ovary contains one or more ovules which each contain an ovum with a female nucleus that a male pollen nucleus can fuse with
Once the nuclei (pl) have joined together, that ovule has been fertilised and a zygote has been formed
The zygote will start to divide and eventually form a seed within the ovule
Growth & Development of the Fetus
After fertilisation in the oviduct, the zygote travels towards the uterus
This takes about 3 days, during which time the zygote will divide several times to form a ball of cells known as an embryo
In the uterus, the embryo embeds itself in the thick lining (implantation) and continues to grow and develop
The gestation period for humans is 9 months
Major development of organs takes place within the first 12 weeks, during which time the embryo gets nutrients from the mother by diffusion through the uterus lining
After this point the organs are all in place, the placenta has formed and the embryo is now called a fetus
The remaining gestation time is used by the fetus to grow bigger in size
The fetus is surrounded by an amniotic sac which contains amniotic fluid (made from the mother’s blood plasma)
This protects the fetus during development by cushioning it from bumps to the mother’s abdomen
The umbilical cord joins the fetus’s blood supply to the placenta for exchange of nutrients and removal of waste products
Explain the placenta and umbilical cord
During the gestation period the fetus develops and grows by gaining the glucose, amino acids, fats, water and oxygen it needs from the mother’s blood
The bloods run opposite each other, never mixing, in the placenta
The fetus’s blood connects to and from the placenta by the umbilical cord
The mother’s blood also absorbs the waste from the fetus’s blood in the placenta; substances like carbon dioxide and urea are removed from the fetus’s blood so that they do not build up to dangerous levels
Movement of all molecules across the placenta occurs by diffusion due to difference in concentration gradients
The placenta is adapted for this diffusion by having a large surface area and a thin wall for efficient diffusion
The placenta acts as a barrier to prevent toxins and pathogens getting into the fetus’s blood
Explain the changes in hormones during menstruation
The pituitary gland produces FSH which stimulates the development of a follicle in the ovary
An egg develops inside the follicle and the follicle produces the hormone oestrogen
Oestrogen causes growth and repair of the lining of the uterus wall and inhibits production of FSH
When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle)
The follicle becomes the corpus luteum and starts producing progesterone
Progesterone maintains the uterus lining (the thickness of the uterus wall)
If the ovum is not fertilised, the corpus luteum breaks down and progesterone levels drop
This causes menstruation, where the uterus lining breaks down and is removed through the vagina - commonly known as having a period
If pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy
Explain protein synthesis
Proteins are made by ribosomes with the sequence of amino acids controlled by the sequence of bases contained within DNA
DNA cannot travel out of the nucleus to the ribosomes (it is far too big to pass through a nuclear pore) so the base code of each gene is transcribed onto an RNA molecule called messenger RNA (mRNA).
mRNA then moves out of the nucleus and attaches to a ribosome
The ribosome ‘reads’ the code on the mRNA in groups of three
Each triplet of bases codes for a specific amino acid
In this way the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein
Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein
Explain the process of mitosis and its importance
Mitosis is defined as nuclear division giving rise to genetically identical cells
Process:
Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x - shaped chromosomes)
Chromosomes line up along the centre of the cell where cell fibers pull them apart
The cell divides into two; each new cell has a copy of each of the chromosomes
Importance:
All cells in the body (excluding gametes) are produced by mitosis of the zygote
Mitosis is important for replacing cells e.g, skin cells, red blood cells and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)
Occurs in:
Growth: mitosis produces new cells
Repair: to replace damaged or dead cells
Asexual reproduction: mitosis produces offspring that are genetically identical to the paren
