unit 1 topic 2 Flashcards
define stem cell
An unspecialised, immature cell capable of differentiating into a specialised cell
1 Stem cells are unspecialised; that is, they have not yet developed into a particular type of cell.
2 Stem cells have the potential to divide and replicate for long periods of time.
3 Although stem cells are relatively unspecialised cells, they can differentiate to form different specialised cells.
define totipotent cell
a stem cell that can develop into any of the types of cells necessary for embryonic development
define pluripotent
a stem cell that can develop into many, but not all, of the cell types necessary for foetal development
define potency
The ability of a stem cell to differentiate into different cell types
what is the hierarchical structure of tissues organs etc
multicellular organisms systems organs tissues cells
what must a good surface exchange area have
◗be moist, because the gases dissolve in water to diffuse from one side of the membrane to the other
◗be thin and permeable, so the gas molecules can move across it easily and quickly
◗have a large surface area in relation to volume of the organism, to adequately supply the gaseous requirements and efficiently remove gaseous waste
◗have a greater concentration of gas to be transported on one side of the membrane than on the other, so that the concentration gradient is maintained
explain the process of respiration in mammals
Air passes into the lungs through the nose and mouth and into the trachea (windpipe), which branches into two bronchi (singular: bronchus) leading into the lungs.
Inside the lungs, each bronchus continually divides into smaller tubes called bronchioles, each of which ends in a cluster of tiny air sacs called alveoli.
Inside the lungs, each bronchus continually divides into smaller tubes called bronchioles, each of which ends in a cluster of tiny air sacs called alveoli.
The wall of the capillary, also only one cell thick, surrounds each alveolus.
Gaseous exchange between the two environments occurs naturally by diffusion: there is a higher concentration of oxygen in the air drawn into the alveolus than in the capillaries, and so oxygen enters the capillaries.
conversely, there is a higher concentration of carbon dioxide in the capillaries than in the inhaled air, and so carbon dioxide molecules diffuse out into the alveolus.
the oxygen entering and dioxide leaving moves down a concentration gradient.
define mechanical digestion
the physical break down and/or mixing of ingested substances, with no chemical change occurring
explain the process of digestion in mammals
Food enters through the mouth, where mechanical digestion first occurs, with the teeth chopping and grinding the food into many smaller pieces.
This physical chewing action creates a much larger surface area of food material upon which the digestive juices, in watery saliva, can better act, in the first stage of chemical digestion.
The tongue carries out the mixing, and moves the food to the back of the throat where it is swallowed into the tubular oesophagus.
The wall of the oesophagus contracts in rhythmic waves to move food into the stomach. Both mechanical and chemical digestion continue in the stomach.
The partially digested food is then released progressively from the stomach into the small intestine, where the bulk and remainder of the chemical digestion takes place to allow passage of nutrients into the body itself.
explain digestion in the small intestine
In the small intestine, nutrients such as glucose, amino acids, fatty acids and glycerol move from the gut (digestive tube) into the blood by diffusion and active transport.
The structure of the small intestine is perfect for the uptake of nutrients.
The lining is moist and thin with a rich supply of blood vessels.
Special structures, known as villi project from the surface of the small intestinal tissue.
Villi are tiny finger-like projections, with walls one cell thick. Villi completely cover the inner intestinal surface.
The epithelial cells that form the villi boundaries, in turn, have a cell membrane that is convoluted into multitudes of microvilli. The villi and their microvilli massively increase the surface area of the gut lining and facilitate efficient absorption
define villus
an elongated projection from the lining of the small intestine that hugely increases the surface area and thus the capacity for exchange of materials
what are the 4 gas exchange features all exchange surfaces have
They are moist
thin
they have a large surface area
and there is a greater concentration of molecules on one side of the exchange surface than on the other.
define proteases
breaks down proteins into amino acids
define lipases
breaks down lipids into fatty acids and glycerol
describe urea and uric acid
In mammals, cells in the liver convert ammonia to the less toxic urea. The urea is carried to the kidneys where it is diluted with water to form urine, which is eliminated from the body.
describe ammonia excretion
Ammonia is the simplest of the nitrogenous wastes produced by protein breakdown. It is extremely toxic, so large quantities of water are required to dilute the ammonia and dissolve it for transport out of the body. Fish are totally surrounded by water in their environment, so they can excrete nitrogenous waste in this form.
describe birds and uric acid
In a terrestrial environment, where water may be scarce, extra energy is expended by liver cells to very quickly convert ammonia to urea. Urea is much less toxic to cells than ammonia.
Therefore, it can be stored longer in the body and in a more concentrated form, so that less water is lost when it is eliminated.
Birds, reptiles and insects excrete it as uric acid, a whitish semi-solid substance.
define nephron
A specialised structural and functional unit within the kidney where elimination of waste molecules from the blood and regulation of solute and water levels occurs
explain how nephrons assist in the kidneys
The glomerulus is situated inside the Bowman’s capsule, which looks like a hollow rubber ball that has been pressed in on one side.
The capillaries that form the glomerulus are tightly bound into the smaller Bowman’s capsule, and the blood pumped into them by the renal artery is under very high pressure.
This pressure forces some of the water, along with all its solutes except large proteins and blood cells, out of the blood through the one-cell-thick glomerulus wall and into the Bowman’s capsule, through its one-cell-thick wall.
The liquid in the capsule is referred to as filtrate.
The Bowman’s capsule connects to the proximal tubule, then to a hairpin-shaped loop of Henle, extending down into the medulla, and finally to the distal tubule.
A collecting duct, the last structural component of the individual nephron, collects the filtrate, now containing wastes, from the distal tubule.
The collecting duct passes down through the medulla, and empties the waste filtrate (urine) into an extensive drainage collection system channelling into the kidney’s central cavity (renal pelvis).
From here, urine passes into the ureter, then the bladder and finally into the urethra, which opens to the outside of the body.
Once the filtrate enters the Bowman’s capsule, it becomes part of the external environment.
All of the useful components of the blood that were forced out of circulation into the Bowman’s capsule are not lost to the external environment. The substances left inside the glomerulus capillaries, including the remaining water, then flow on into a branching network of capillaries threading around the nephron’s tubular parts.
Water and solutes required by body cells are reabsorbed from the nephron tubules into the surrounding capillaries, which converge into a branch of the renal vein.
define stoma
a controlled opening found in leaves and young stems that controls the movement of gases into and out of a plan
define guard cells
a pair of crescent-shaped cells that enable the opening and closing of a stoma
define stomata
a stoma is a tiny pore in the surface of a leaf that is used for gas exchange.
define cuticle
a thin, transparent layer of wax on the outside of a leaf’s epidermis to reduce water loss
