organisation Flashcards
this is a massive topic, i'm so sorry
what are cells?
the basic building blocks of all living organisms.
- all sorts of shapes and sizes
- contain different combinations and numbers of organelles
- different types of cells are specialised cells
what is a tissue?
a group of similar cells that work together to carry out a particular function.
- e.g. muscle cells form muscle tissue. they contract and relax to move different parts of the body.
what is an organ?
a group of different tissues that work together to carry out a particular function.
- e.g. epithelial, muscle, and glandular tissue all work together to form the stomach, which has the function of killing microorganisms and breaking down proteins.
what is an organ system?
a group of organs that work together to perform a particular function
- e.g. the stomach, pancreas, liver (and others) come together to form the digestive system, which has the role of digesting the food we eat and absorbing nutrients
what is the level above an organ system?
the organism, with many different organ systems working together to form the organism
what are the three main nutrients in food, and how are they absorbed into the bloodstream?
- carbohydrates (e.g. starch), protein, and lipids (fats)
- all of these are large molecules and are too large to be absorbed into the bloodstream, and so have to be digested.
- enzymes break down these molecules into smaller molecules, which can then be absorbed into the bloodstream.
describe carbohydrates:
found in starchy foods (bread, pasta, potatoes). used as an energy source for chemical reactions and movement
- molecules made from carbon, hydrogen, oxygen
- smallest carbs are simple sugars (glucose, fructose): monomers. these can join together to form polymers (glycogen, starch)
- in a complex carb, there are chemical bonds between the monomers, which can be broken to change the complex carb into a simple carb (starch broken down into glucose)
describe lipids:
- refers to both fats and oils
- found in oily fish, nuts and seeds, dairy products, avocados
- provide energy, but act as a longer term store
- also keep us warm through insulation, protect our organs
- contain a single glycerol molecule connected to three fatty acid molecules. these are usually different lengths, and the length determines whether the lipid is a fat or an oil
- made from carbon, hydrogen and oxygen atoms
describe proteins:
- nuts and seeds, meats and fish
- need them to grow, repair damaged tissue
- can also be used for energy, but only in emergencies
- long chains of amino acids bonded together (a polymer). the amino acid is a monomer
- amino acids are mainly made from carbon, hydrogen, oxygen and nitrogen atoms
describe vitamins and mineral ions:
- many different types, only needed in small amounts
- vitamins are organic molecules (made by living organisms), minerals are inorganic
- vitamins include vitamin a, c, d (better vision, etc.)
- minerals include calcium and iron (for stronger bones, iron is essential in helping red blood cells to transport oxygen)
describe fibre:
- type of carbohydrate, but thought of as separate as it’s not absorbed into the body
- wholemeal foods, fruit and veg
- helps food move through our intestines properly
describe water:
- from drinks, most foods
- chemical reactions, most of our body is made of water, and we’re continuously losing water by breathing, sweating, urinating, so we must constantly replace it
describe stage 1 of the digestive pathway, the mouth:
TEETH:
- physically/mechanically break down food by chewing
- increases surface area of food, making it easier for enzymes to break it down, and makes the food easier to slow
SALIVARY GLANDS:
- release saliva, a watery mix containing amylase. the water wets the food, making it easier to swallow, the amylase digests the starch into maltose
describe stage 2 of the digestive pathway, the stomach:
has now passed through a muscular tube in the throat, the oesophagus.
the stomach:
- CONTRACTS ITS MUSCULAR WALLS, churning and mixing up the food
- PRODUCES PEPSIN (protease enzyme), breaking the protein down
- PRODUCES HYDROCHLORIC ACID, killing bacteria and providing the right pH for pepsin
describe what happens at the same time as the food is in the stomach, in the gallbladder and pancreas:
PANCREAS: releases pancreatic juices into the small intestine. it’s a liquid mixture containing amylase, protease, lipase and more
GALLBLADDER: releases bile into the small intestine. bile is made in the liver, however, and only stored in the gallbladder
1. neutralises the stomach acid, as it’s alkaline, making the pH more ideal for the function of digestive enzymes
2. emulsifies lipids, giving the lipids a much larger surface area for digestive enzymes to work on
there’s now a mix of food, pancreatic juices and bile in the small intestine together, as the stomach has now contracted greatly and pushed the food through
describe stage 3 of the digestive pathway, the small intestine:
- IT’S WHERE MOST OF THE DIGESTION TAKES PLACE
- releases digestive enzymes, like carbohydrase, lipase and protease
- all of the nutrients are now broken down - IT’S WHERE MOST OF THE NUTRIENTS ARE ABSORBED INTO THE BLOODSTREAM
- surface covered in tiny finger-like projections called villi, allowing all useful nutrients to be absorbed into the bloodstream
describe stage 4 of the digestive pathway, the large intestine/colon, rectum and anus:
- colon absorbs most of the excess water into the bloodstream
- leaves a dry mixture (faeces) which is stored in the rectum until it can be released through the anus
what is the role of the digestive system?
DIGESTION: the process by which we break down the large food molecules that we eat into much smaller molecules
ABSORPTION: the process by which we absorb these small molecules, along with vitamins, minerals and water from the digestive tract into the bloodstream, to be sent around the body and used
what are the different large molecules broken down into, and what are the names of the enzymes that break them down?
- carbohydrates (including starch, a polymer of glucose) - simple sugars
CARBOHYDRASE (E.G. AMYLASE BREAKS
DOWN STARCH INTO MALTOSE
MOLECULES, WHICH ARE TWO GLUCOSE
MOLECULES STUCK TOGETHER. Maltase
then breaks down maltose, into glucose,
which is now small enough ) - proteins
PROTEASE (group of enzymes, including
specific ones like trypsin and pepsin)
> in digestion, they’re broken down
into individual amino acids, and once
absorbed into the bloodstream, they’re
joined together in a different order to
make human proteins. - lipids (fats)
LIPASE
why is digestion needed?
- carbs, proteins and lipids are big molecules and too big to be absorbed into our bloodstream
- they must be broken down into much smaller pieces, using enzymes
describe enzymes and how they work:
- enzymes catalyse chemical reactions (biological catalysts, as it’s made by living organisms)
- they are large protein molecules, with a groove on their surface called the active site.
- the active site is where the substrate attaches to - the substrate is the molecule that the enzyme breaks down. the active site is complementary to the enzyme’s specific substrate
- the enzyme will have a unique shape, depending on the shape the amino acid chain has folded up into
what allows enzymes to be specific about which reactions they speed up?
if the substrate doesn’t fit into the enzyme’s active site, it won’t catalyse the reaction
what is a catalyst?
a substance that increases the speed of a chemical reaction without being changed or used up in the process
why can’t we simply catalyse the slow chemical reactions in our body by increasing the temperature?
- requires a lot of energy to increase the temperature across the entire organism
- high temperatures can damage our cells
- high temperatures will also speed up non-useful reactions, that we don’t want to happen
describe the ‘lock and key’ theory:
scientists thought the substrate had to fit perfectly into the active site (like how a key fits perfectly into a lock), in order for the enzyme to be catalysed
describe the (more realistic) induced fit model:
the enzyme actually changes shape slightly as it binds to the substrate, so they can fit together more perfectly
where are the different biological molecules broken down by enzymes?
amylase - mouth, small intestine
protease - stomach, small intestine
lipase - small intestine
describe bile:
- made in the liver, stored in the gallbladder.
- speeds up the digestion of lipids BUT is not an enzyme.
- bile emulsifies lipids, increasing the surface area of lipid droplets (by breaking down big droplets of lipids) and increasing the rate of digestion by lipase.
- bile is alkaline. neutralises the acidic conditions (from hydrochloric acid) in the small intestine and the stomach. the alkaline conditions and large surface area increase the rate of lipid digestion by lipase.
where is each enzyme made?
amylase: pancreas, small intestine, salivary glands
protease: pancreas, small intestine, stomach
lipase: pancreas, small intestine
what is the effect of temperature on enzymes?
- initially, the activity of the enzyme increases as the temperature increases - the enzyme and the substrate are moving faster, so there are more collisions per second between the enzyme and the active site.
- however, the enzyme will reach the optimum temperature (37 degrees celsius for more human enzymes). after this temperature has been surpassed, the activity of the enzyme rapidly decreased to 0.
- these high temperatures have denatured the enzyme, and the changed the shape of its active site, as some of the bonds holding the enzyme together have been broken. now the substrate doesn’t fit perfectly anymore, and enzyme can no longer catalyse the reaction.
what is the effect of pH on enzymes?
- the enzyme has an optimum pH, where the activity is maximum.
- if we make the pH more acidic or more alkaline, then the activity drops to 0, as the enzyme has denatured, the active site has changed shape (some of the bonds holding the enzyme together have started to break).
- each enzyme has a specific optimum pH. protease enzymes, for example, work best at an acidic pH.
- at first, the active site will only change shape a little bit, so the substrate can still fit, but less well. then the active site will change shape so much that the substrate no longer fits at all
what is pH?
a measure of acidity
how is the small intestine adapted to absorb the products of digestion into the bloodstream?
- very long. provides a large surface area for absorption of the products of digestion.
how are villi adapted to absorb the products of digestion into the bloodstream?
- the interior of the small intestine is covered with millions of villi, which increase the surface area for the absorption of molecules.
> the villi are covered with micro-villi,
increasing the surface area even more.
> villi have a good blood supply, so the
bloodstream rapidly removes the
products of digestion. this maintains a
high concentration gradient, and
increases the rate of diffusion/active
transport.
> very thin membrane, single layer of
cells, ensuring a short diffusion path.
what is the structure and function of the heart?
structure:
- four chambers (left and right atrium, left and right ventricle). the atria are separated from the ventricles by atrioventricular valves, which ensure that blood only flows in one direction.
- four main blood vessels.
> vena cava. brings deoxygenated
blood from the body.
> pulmonary artery. deoxygenated
blood passes from the heart to the
lungs.
> pulmonary vein. oxygenated blood
passes from the lungs to the heart.
> aorta. oxygenated blood pumped
from the heart to the body.
what is the path of blood through the heart?
- deoxygenated blood enters through the vena cava from the body into the right atrium.
- the atrium contracts, forcing blood through a valve into the right ventricle.
- the blood is taken from the right ventricle, through the pulmonary artery, to the lungs, where it becomes oxygenated. - the now oxygenated blood enters into the left atrium through the pulmonary vein from the lungs.
- the atrium contracts again, forcing it through the valve into the left ventricle.
- the blood is carried out of the left ventricle and pumped into the body by the aorta.
what is the purpose of a valve in the heart?
prevents the blood from flowing back into the atria during contraction.
why does the left side of the heart have a thicker, muscular wall than the right side?
the left ventricle pumps blood around the entire body, so it needs to provide a greater force. the right ventricle only needs to pump blood to the lungs.
what are coronary arteries?
- branch out of the aorta and spread across the heart muscle.
- provides oxygen to the muscle cells of the heart (this oxygen and nutrients is used in respiration to provide energy for contraction in the muscle tissues).
how is the natural, resting heartrate controlled?
controlled by a group of cells in the top of the right atrium, called the ‘pacemaker’.
- if the natural pace maker stops working, doctors can plant an artificial pacemaker, which corrects irregularities in the heart rate.
describe the lungs:
- provide an exchange surface adapted for:
- absorbing oxygen (for respiration) into the blood from the air.
- transferring carbon dioxide (produced by respiration) from the blood, into the lungs, then the air. - this transfer of gases is called gaseous exchange.
why do we need the lungs?
all cells must carry out cellular respiration, and for that they need oxygen. the lungs get the oxygen we need from the air around us into our bloodstream, to be transported to the rest of the body
describe the structure of the respiratory system:
- adapted to allow air to pass in and out of the body, and to allow efficient gas exchange to occur.
- lungs enclosed in the thorax, protected by 12 pairs of ribs.
- ribs are moved by two sets of intercostal muscles.
- there is a muscular diaphragm beneath the lungs.
- the trachea branches into two bronchi. rings of cartilage in the walls of the lungs help to keep it open as air draws in.
- the bronchi split into smaller branches and then into smaller tubes called bronchioles - these all end in a cluster of microscopic air sacs called alveoli.
describe the process of gaseous exchange in the alveoli:
- occurs between the alveoli and the blood in the capillaries that supply the lungs. capillaries cover 70% of the outside of the alveoli, providing a large surface area for gases to diffuse across.
- each of the alveoli is a small sphere, giving it a large surface area : volume ratio. there are around 700 million alveoli.
- blood flows from the heart across the alveoli, carbon dioxide diffuses out of the blood and into the alveoli, and oxygen diffuses out of the alveoli and into the blood - the blood then returns to the heart.
how has gaseous exchange been made efficient in the alveoli?
- large surface area (see different flashcard)
- short diffusion path (walls of alveoli and capillaries are one cell thick), increasing rate of diffusion
- alveoli lined with thin film of moisture. gases dissolve in this water, increasing the rate of diffusion
- the ventilation of the lungs and the blood flow through the surrounding capillaries means gases are being removed continually, and steep concentration gradients are set up for gases to diffuse (haemoglobin has given away all of its oxygen, so contains hardly any).
- the carbon dioxide is in a higher concentration in the blood plasma than the alveoli, so it can easily diffuse across and be exhaled
how do you calculate breathing rate?
number of breaths taken / time in minutes
- the unit is breaths per minute
which organ system are the lungs a part of?
the respiratory system
describe the structure and function of arteries:
- carries high pressure blood from the heart to the rest of the body.
- very thick, strong muscular tissue walls, to withstand high pressures.
- surges of blood pass through the arteries when the heart beats. elastic fibres/tissue stretch when the surge of blood passes through, and then recoil in between surges, keeping the blood moving
- the wall of the artery is very thick compared to its lumen (the space in the middle). narrow lumen keeps the blood pressure high
what is the circulatory/cardiovascular system?
- example of an organ system
- made up of the organs: heart (pumps the blood, ensures it keeps flowing through the vessels) , blood vessels (hold the blood and direct it around the body), blood (fluid that carries all the substances, e.g. oxygen, nutrients, cells, waste)
- function is to transport substances around the body
what is a double circulatory system?
contains 2 separate circuits:
- pulmonary circuit (blood flows from the heart, around the lungs, and back to the heart again)
- systemic circuit (blood flows from heart, around to all the bodily tissues, and then back to the heart)
describe the structure and function of capillaries:
- exchange substances with cells, giving them useful nutrients and oxygen, and taking away waste products such as carbon dioxide
- very thin walls (single cell), allowing rapid diffusion due to a short diffusion pathway, and permeable walls
- very small vessels
- individual capillary lumen is tiny, but there are so many that their cross-sectional area is huge
- lower, slower-flowing blood, giving the vessels more time to exchange things with tissues
describe the structure and function of veins:
- carry blood from the body to the heart.
- thin walls, of thin layers of elastic fibres and smooth muscle. the blood pressure is low, so thick, strong walls aren’t required.
- contains valves. stops blood from flowing backwards.
> when blood is flowing in the correct
direction, the valves open to allow blood
through. when the blood starts to flow
backwards, the valves shut. - biggest lumen
how do you calculate rate of blood flow?
divide how much blood has flowed by the time it took
what are red blood cells (structure and function)?
- carries oxygen from the lungs to our body’s tissues, for cellular respiration.
- contain haemoglobia, which combines with oxygen to become oxyhaemoglobin. once the blood reaches tissues, the oxygen and haemoglobia can split apart, to allow oxygen to diffuse into cells.
- don’t have a nucleus - more space for haemoglobin and oxygen.
- shaped like a bi-concave disk. large surface area for absorbing oxygen.
what are white blood cells (structure and function)?
- defends and protects us against infection.
> phagocytosis. the cell engulfs a
pathogen.
> producing antibodies. bind onto
pathogens and destroy them.
> producing antitoxins. neutralise toxins
that pathogens may produce. - do have a nucleus.
what are platelets (structure and function)?
- not cells, just small fragments of cells, so don’t have a nucleus.
- float around in our blood until we get a cut, when they rush to the wound and act like a glue, patching up the hole. ‘CLOTTING’.
- stops blood from escaping us, and prevents microorganisms from getting in, as they could cause an infection.
what is plasma (structure and function)?
- pale, straw-coloured liquid, makes the blood watery so that it can flow
- carries everything (including red and white blood cells, platelets) and nutrients, such as glucose, amino acids, waste products, hormones, proteins, antibodies and antitoxins
describe artificial blood:
- artificial blood (basically salt water). adds volume to our circulatory system, keeping our vessels full, and allowing our heart to keep pumping. doesn’t contain any red blood cells though, meaning it can’t transport any oxygen.
describe a blood transfusion:
- a person is given real blood that’s been donated by blood donors.
- includes red blood cells, which is the key to surviving blood loss.
- the blood must be compatible with the patient’s blood type, though.
what are cardiovascular diseases?
- diseases of the heart and blood vessels.
- non-communicable (not infectious).
- examples include: coronary heart disease, heart attacks, faulty valves, and heart failure
describe coronary heart disease:
- layers of fatty material build up inside the coronary arteries, causing the lumen to narrow, so less blood can flow through
- this results in a lack of oxygen to the coronary arteries (and the heart), which puts strain on the heart and could result in a heart attack.
what are statins, how can they treat coronary heart disease, and what are their pros and cons?
- alters the balance of cholesterol (type of lipid) in the blood. two types: LDL (bad), and HDL (good). too much LDL causes fatty deposits in the arteries, and HDL gets rid of fatty deposits
- slows down the rate that fatty material builds up in the arteries.
- PROS: effective treatment, not only lowers risk of CHD but also many other diseases (strokes, heart attacks)
- CONS: can cause side effects (liver problems, headaches and kidney failure), you have to take statins for the rest of your life.
what are stents, how can they treat coronary heart disease, and what are their pros and cons?
- a stent is an expandable tube which is inserted into a coronary artery to keep it open, so blood can keep flowing
- PROS: relatively quick surgery, lasts a long time
- CONS: doesn’t prevent other regions of the coronary artery from being blocked. doesn’t treat the underlying cause of the disease (too much cholesterol in the blood), surgery has risks (induce a heart attack, or lead to infection). can lead to a blood clot near the stent: ‘thrombosis’
what are other examples of diseases of the heart, caused by the valves, and how can we treat them?
- the heart valves sometimes don’t fully open, so the heart has to pump extra hard to get the blood through, enlarging the heart.
- the valves sometimes also don’t close fully, so can be leaky, causing the patient to be weak or tired.
- can replace the valves with a mechanical valve. these last a lifetime but can cause blood clots, so patients have to take anti-clotting drugs. requires surgery
- can also treat with animal (biological) valves (e.g. pigs), however, these may need to be replaced. on the other hand, patients don’t need to take drugs. requires surgery
what is heart failure?
where the heart can’t pump enough blood around the body. these patients are sometimes given a donated heart, or heart and lungs.
what are the disadvantages to the use of donor hearts?
- there aren’t enough donated human hearts to treat every patient.
- the patient must take immunosuppressant drugs to stop the heart from being rejected from the body’s immune system, otherwise it may see the heart as foreign and try to destroy it
describe artificial hearts, and their pros and cons:
- a temporary solution while waiting for a heart transplant, or to allow their damaged heart to rest.
- artificial hearts increase the risk of blood clotting, and can only be used for a relatively short time.
- isn’t rejected by immune system, as it’s made of metals and plastics
define health:
a state of physical and mental wellbeing
how do you maintain good health, and how can you become unhealthy?
good health:
- good, balanced diet
- sufficient exercise/sleep
- access to medical care (e.g. vaccines)
bad health: (can result in illness)
- none of the above
- too much stress
- disease, both communicable and non-communicable
define disease:
a large group of conditions that cause ill health
what is the difference between a communicable and non-communicable disease?
- communicable: can spread from person to person, or between animals and people. INFECTIOUS. can be caused by viruses, bacteria, parasites and fungi.
> common cold, malaria, meningitis - non-communicable: can’t be spread between people. not caused by pathogens. these start more slowly and last a long time (some never go away)
> asthma, coronary heart disease,
diabetes, cancer.
what are 4 examples of different types of diseases that interact?
- defects in the immune system mean that an individual is more likely to suffer from communicable diseases.
- viruses living in cells can be the trigger for cancers. for example, HPV (human papilloma virus) can cause cervical cancer in women
- immune systems can overreact to pathogens (e.g. skin rashes, asthma), ending up damaging our own tissues instead
- severe physical health problems can lead to depression, chronic anxiety, and other mental illnesses, especially if they impact a person’s ability to carry out their day to day tasks.
what is the role of the immune system?
to detect and destroy pathogens
what are the lifestyle factors that can increase the risk of non-communicable diseases?
this is a big card, good luck!
- a diet high in fat and low in vegetables can increase the levels of types of cholesterol in the blood, leading to a build up of fatty material in the arteries, and can also lead to type 2 diabetes
- a diet high in salt can increase blood pressure, increasing the risk of cardiovascular diseases.
- smoking increases the risk of cardiovascular disease, lung cancer, lung disease and emphysema.
> cigarette smoke contains carcinogens,
which can trigger cancer.
> the toxins in the smoke directly
damage the walls of the blood vessels
and the cells lining the lungs - excessive alcohol consumption can increase the risk of liver cirrhosis, liver disease and liver cancer. it can also lead to addiction and memory loss.
- excessive exposure to radiation can increase the risk of developing lung cancer, and asbestos can also cause cancer.
how can smoking and alcohol consumption during pregnancy harm the baby?
- smoking increases the risk of miscarriage and premature birth, or of the baby being born with a low body mass.
- alcohol consumption can cause foetal alcohol syndrome. children born with this can have learning difficulties or other mental an physical problems.
describe the wider impact of disease:
- when someone is ill, they’ll rely on family and friends for support, and if they’re really ill, they’re unable to work. their whole family is now poorer
- if there’s more disease nationally, the workforce will be less productive, and a bigger share of Government spending will have to be spent on health
what is COPD (chronic obstructive pulmonary disease)?
- lung disease characterised by irreversible lung damage and an obstructed airway
- people suffering from it will find it very difficult to breathe
- smoking is the primary risk factor, and the risk increases with the duration and intensity of the smoking
which two illness does COPD refer to?
people with it will often have both of these diseases:
- BRONCHITIS: inflammation of the bronchi and bronchioles, leading to increased mucus production and coughing
- EMPHYSEMA: damage to the alveoli walls, leading to fewer larger alveoli, instead of many smaller ones. this reduces the surface area available for gas exchange
what are the two categories a risk factor typically falls into?
- aspects of a person’s lifestyle
- substances in the person’s body/environment
describe type 2 diabetes and its implications:
- when the body struggles to control its blood glucose levels.
- can lead to blindness, or require the amputation of a limb.
- obese people have a much bigger risk of developing type 2 diabetes.
what is cancer?
a disease caused when abnormal cells grow uncontrollably and spread to other parts of the body
what is a tumour, and what is the difference between a benign and malignant tumour?
- an abnormal mass of cells, where they’ve undergone uncontrolled growth and division.
- benign tumour: group of cells are controlled in one area, usually a membrane. so they’re not normally dangerous, and aren’t called cancer.
- malignant tumour: don’t stay in one place. enter the bloodstream, invade other tissues, and spread to different parts of the body, where they can form secondary tumours. these are very dangerous, and potentially fatal. they’re classified as cancer.
what are the risk factors associated with cancer?
- smoking is mainly linked to lung cancer. it’s also linked to mouth, stomach and cervical cancer.
- obesity is linked to bowel, liver, and kidney cancer.
- ultraviolet light exposure (from sun and sunbeds) is linked to skin cancer, as the UV rays damage our skin cells.
- drinking alcohol is linked to an increased risk in liver cancer.
- sometimes not all of the cancer risk factors are due to our lifestyle. some can be genetic.
> the BRCA genes are linked to breast
and ovarian cancer in women.
what are the top and bottom layers of a leaf called?
the upper and lower epidermis.
- very thin cells (epidermal cells forming epidermal tissue).
- protects the surface of the leaf.
- the upper epidermis is transparent, allowing light to pass through to the photosynthetic cells below.
- the upper epidermis is also covered with the waxy cuticle (oily material), which reduces the evaporation of water from the surface of the leaf.
- lower epidermis is covered with tiny pores - stomata. they allow carbon dioxide to enter the leaf, and oxygen to leave. controls the amount of water vapour passing out of the leaf.
is the leaf an organ?
yes, along with the stem and the roots
what is the function of a leaf?
site of photosynthesis
- requires carbon dioxide and water to make sugars
- water comes from the soil and is transported to the leaves via the roots and xylem
- the carbon dioxide diffuses directly into the leaf from the outside air via the stomata
what is the role of the palisade mesophyll?
- consists of palisade cells
- packed full of chloroplasts, and near the surface, meaning that photosynthesis can occur.
what is the role of the spongy mesophyll?
- full of air spaces.
- the air spaces allow carbon dioxide to diffuse from the stomata through the spongy mesophyll to the palisade cells.
- oxygen also diffuses from the palisade cells, through the spongy mesophyll, to the stomata.
what is the role of xylem tissue in the leaf?
transports water from the roots to the stem and the leaves. some of the water is then used in photosynthesis. transports dissolved mineral ions (e.g. magnesium), which is used to make chlorophyll.
describe xylem tubes:
made up of columns of dead xylem cells with no ends between them, forming one long hollow tube
- strengthened with lignin
- transport water and mineral ions from the roots, up the stem to the leaves for photosynthesis
what is the role of phloem tissue in the leaf?
transports dissolved sugars produced by photosynthesis from the leaves to the rest of the plant.
- these sugars can be used immediately (e.g. glucose can be used in respiration)
- these sugars can be stored (e.g. as starch)
- THIS IS CALLED TRANSLOCATION
describe phloem tubes:
phloem cells are arranged end to end and form long columns called phloem tubes
- in between adjacent cells, lots of small pores, which enable the movement of cell sap (liquid mixture of water and sugar)
- transports substances in either direction
what are sugars used for in the plant?
- either immediately used for energy
- or stored for later
how do guard cells work to control stomata?
- when the plant has lots of water, so it doesn’t have to worry about conserving it, the guard cells will be well-hydrated (turgid).
- this make the gap between them larger, allowing more carbon dioxide to diffuse through.
- when the plants don’t have a lot of water, the guard cells will lose water, due to osmosis. they’ll become flaccid, and close the gap.
- the plant no longer takes in carbon dioxide, and will conserve its water vapour.
how do guard cells respond to light?
guard cells are sensitive to light, and close at night-time, when photosynthesis isn’t taking place, and so the leaf doesn’t require carbon dioxide. therefore its only priority is to conserve water.
why are stomata on the underside of the leaf?
the underside is more shaded, making it cooler. this means that less water will evaporate, conserving water.
what is transpiration?
the process of water movement through plants, and its evaporation from certain parts (e.g. leaves)
> this evaporation cools the leaf down,
especially in warm weather.
how is a constant water supply maintained in the leaf?
- water vapour diffuses through the gaps in the spongy mesophyll and out through the stomata - transpiration
- water passes from the xylem into the leaf, to replace the water that’s been lost.
- finally, water is drawn into the root hair cells and up the xylem vessels to the leaf.
THE TRANSPIRATION STREAM
what are the factors that affect the rate of transpiration?
- higher temperatures increase the rate of transpiration (evaporation is faster at higher temperatures, as the particles have more energy).
- dry conditions (e.g. not humid) also increase the rate of transpiration. evaporation takes place quicker under dry conditions, due to a bigger concentration gradient.
- windy conditions increase the rate of transpiration. wind removes surrounding water vapour, allowing more evaporation to occur as the concentration remains high
- increased light intensity increases the rate of transpiration as this increases the rate of photosynthesis. this means the stomata have opened to allow carbon dioxide in. once they’ve opened, water vapour can pass out of the leaf.
what is a balanced diet?
- includes appropriate portions of all the different biological molecules: (carbohydrates, lipids, proteins, fibres, water, vitamins, minerals)
- too much or too little could lead to problems
what are the three main things to consider when deciding how much energy we need (measured in calories)?
- activity level: the more active, the more energy you need
- age: teenagers need more energy as they’re growing, the elderly need less
- pregnancy: pregnant women need more energy as the baby growing inside requires lots of energy
