B2 - Organisation Flashcards
What is a Organelle?
Organelle - A specialised unit within a cell which performs a specific function
What is meant by organisation?
- Cells are the basic building blocks of all living organisms
- Unicellular organisms are made from one cell, whereas multicellular organisms are made up of collections of cells
- In complex multicellular organisms, cells are specialised to carry out particular functions. These specialised cells form tissues, which form organs in organ systems
- In humans, the digestive system (provides the body with nutrients) and the respiratory system (provides the body with oxygen and removes carbon dioxide) are examples of organ systems that provide dissolved materials that need to be moved quickly around the body in the blood by the circulatory system
Why do we need exchange surfaces?
Organisms must take in food,oxygen and water, and other essential substances, from the environment. Plants also need carbon dioxide for photosynthesis. Organisms also need to remove waste substances.
Small organisms exchange these essential and waste substances between themselves and the environment. They do this over their body surface. Simple chemical substances can diffuse in and out of their bodies.
Inside their bodies, in small organisms, substances don’t have to move far.
The size of their surface, or surface area, defines how quickly they can absorb substances. The size of their volume defines how much of these substances they need.
What are the problems with animals increasing in size?
As the volume increases, surface area does not increase at the same rate.
As multicellular organisms increase in size, they face two problems:
How is the effectiveness of exchange surfaces in plants and animals increased?
The effectiveness of exchange surfaces in plants and animals is increased by having:
A large surface area:
- the flattened shape of structures such as leaves
- the alveoli in the respiratory system
- the villi in the digestive system
A short distance required for diffusion:
- the membranes of cells
- the flattened shape of structures such as leaves
- the walls of blood capillaries are one cell thick
- the epithelia of alveoli in the respiratory system and the villi in the small intestine are only one cell thick
Animals have additional adaptations for effective exchange surfaces
An efficient blood supply to transport molecules to and from the exchange surface increases effective exchange. Examples of this include:
- the network of blood capillaries that surrounds each alveolus in the lungs
- the network of blood capillaries in each villus in the small intestine
The process of breathing, or ventilation, brings air to, and removes air from the exchange surface – the alveoli.
The moving blood and ventilated surfaces mean that a steep concentration gradient can be maintained. This increases effective exchange.
What are the human lungs adapted for?
The human lungs provide an exchange surface adapted for:
- absorbing oxygen – needed for respiration – into the blood from the air
- transferring carbon dioxide – produced by respiration – from the blood into the lungs then the air
The lungs are organs enclosed within the chest or thorax. Air needs to be breathed in to be brought into contact with the exchange surfaces within the lungs. This process is called ventilation.
How is the respiratory system structured?
The structure of the respiratory system
The human respiratory system is adapted to allow air to pass in and out of the body, and for efficient gas exchange to happen.
The lungs are enclosed in the thorax, surrounded and protected by 12 pairs of ribs. The ribs are moved by two sets of intercostal muscles. There is a muscular diaphragm below the lungs. The lungs are sealed within two airtight pleural membranes. These wrap around the lungs and line the rib cage.
The trachea, or windpipe, branches into two bronchi – one bronchus to each lung. Rings of cartilage in the walls of the trachea help to keep it open as air is drawn in.
The bronchi split into smaller branches and then into smaller tubes called bronchioles. Each bronchiole ends in a cluster of microscopic air sacs called alveoli.
How is the alveoli adapted to provide a very large surface area for gas exchange?
The alveoli are adapted to provide a very large surface area for gaseous exchange:
- small size - each alveolus is a small sphere about 300 μm in diameter, giving it a larger surface area to volume ratio than larger structures
- number - there are around 700 million alveoli – ie 350 million per lung
- The total surface area of the alveoli is around 70 square metres.
- There is also a short diffusion path - the walls of blood capillaries and alveoli are just one cell thick. The alveoli are also lined with a thin film of moisture. Gases dissolve in this water, making the diffusion path even smaller.
- The ventilation of the lungs and the blood flow through the surrounding capillaries mean gases are being removed continually, and steep concentration gradients are Maintained
What is Ventilation?
Ventilation
Air is moved into and out of the lungs, as it is carried to and from the exchange surfaces of the alveoli.
The diaphragm and rib cage move to create a lower air pressure in the lungs than that of the air outside the body. Air then rushes into the lungs.
The most important muscle when we inhale normally is the diaphragm. The external intercostal muscles are the second most important muscles. Breathing is a passive process resulting from pressure changes in the lungs.
What happens when we breathe in?
When we inhale
- Diaphram contracts
- The Intercostal muscles Contract
- the ribs move upwards and outwards
- Volume of throax increases so pressure decreases and air is drawn into the lung
What happens when we breathe out?
Breathing in
When we exhale
- The diaphram relaxes and moves up
- The intercostal muscles relax so the ribs move downwards and outwards
- the volume of the thorax decreases so pressure increases and air leaves the lungs.
Why do fishes have different exchange system?
Water is capable of holding only low concentrations of oxygen, so fish need a different type of exchange system.
The exchange surfaces in fish are gills.
How does gas exchange occur in fishes?
- Water is taken in through the fish’s mouth, passes over the gills, and then out under the operculum
- Each gill filament has a network of blood capillaries
- Water that flows over the gills flows in the opposite direction to the blood. This is called counter current flow. It means that the exchange of oxygen and carbon dioxide is more efficient than if the water and blood were both flowing in the same direction.
Why is gas exchange very efficient in fishes?
Exchange of gases in fish is very efficient because of:
- the large surface area of the gills
- the large surface area of the blood capillaries in each gill filament
- the short distance required for diffusion – the outer layer of the gill filaments and the capillary walls are just one cell thick
- the efficient ventilation of the gills with water - there is a counter current flow of water and blood
The moving blood and ventilated gill surfaces mean that gases exchanged are continually removed – oxygen enters the blood, and carbon dioxide removed to the water. High concentration gradients can be maintained.
Illustrate the different levels of organisations in the stomach?
- We can illustrate different levels of organisation by looking at the stomach:
- The role of the stomach is to start protein digestion
- To do this, the stomach produces proteases like pepsin, which digests proteins into amino acids.
- Acid produced by glandular tissue in the stomach aids protein digestion; it helps proteins unravel so that enzymes can break the bonds holding the amino acids together. It also inhibits many microorganisms that may be present in food, reducing the chance of infection
- The stomach is one of a number of organs that make up the digestive system
- The role of the digestive system is to break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients
What are the major nutrients that humans need and how do we obtain it?
Carbohydrates, proteins, lipids (or fats) are major nutrients that we need in large quantities.
We get these by eating them. They are broken down first and then reassembled into our own carbohydrates, proteins and lipids. This is because:
- most of the molecules in food are too large to pass through the absorbing surface of the gut wall
- the carbohydrates, proteins and lipids are reassembled in the form required, rather than other animal or plant versions
What is the Major function of Carbohydrates?
What is the Major source of Carbohydrates?
Nutrient: Carbohydrates
Major Function: Source of energy, glucose is the main respiratory substrate.
Major sources:
Starch: potatoes, rice and wheat products, bread, cereals and pasta.
Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets
What is the Major function of Proteins?
What is the Major source of Proteins?
Nutrient: Protein
Major Function: Growth and repair
Major sources:
Meat, eggs, cheese, beans, nuts and seeds
What is the Major function of Lipids?
What is the Major source of Lipids?
Nutrient: Lipids
Major Function: Storing Energy
Major sources:
Butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds
What is digestion?
- Digestion is a process in which relatively large, insoluble molecules in food (such as starch, proteins) are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body
- These small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy (via respiration), or with materials with which they can build other molecules to grow, repair and function
What is the alimentary canal?
- The human digestive system is made up of the organs that form the alimentary canal and accessory organs
- The alimentary canal is the channel or passage through which food flows through the body, starting at the mouth and ending at the anus. Digestion occurs within the alimentary canal.
- Accessory organs produce substances that are needed for digestion to occur (such as enzymes and bile) but food does not pass directly through these organs
Explain the digestive process from beginning to end?
First, food is chewed in the mouth. Enzymes(amylase) begin to digest the starch into smaller sugar molecules into maltose to increase its SA:V ratio.
Then food passes down into the stomach. Through the oesophagus which will contract to push the food down without relying on gravity
In the stomach, enzymes(protease) begin the chemical digestion of proteins.
The stomach also contains hydrochloric acid which helps the enzymes to digest proteins as it provides the optimum pH for enzymes to work.
The food spends several hours in the stomach and the churning action in the stomach muscles turns the food into a fluid increasing the surface area for enzymes to digest.
The fluid now passes into the small intestine from the liver to the pancreas.
The pancreas produces all three types of digestive enzymes which continue the digestion of Starch & protein. It also starts the digestion of lipids.
The liver releases bile which helps speed up the natural digestion of lipids. Bile also neutralises the acid released from the stomach. Amino acids not used to make protein are broken down in the liver which produces urea.
The walls of the small intestines release enzymes to continue the digestion of protein and lipids. In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or by active transport.
Now the fluid makes its way through the large intestine, where water is absorbed into the bloodstream.
Finally faeces are released through the anus.
Why is bacteria important in digestion?
- The large intestine is home to hundreds of species of bacteria
- These bacteria form a microbial ecosystem (the microbiota, or gut flora) that play an essential role in human digestion of food by:
- Breaking down substances we can’t digest (like cellulose)
- Supplying essential nutrients
- Synthesising vitamin K
- Providing competition with any harmful bacteria to restrict their growth
- Taking antibiotics can disrupt the gut microbiota which can cause short-term problems with digestion
What are Enzymes?
What is Metabolism?
- Digestive enzymes work outside of cells; they digest large, insoluble food molecules into smaller, soluble molecules which can be absorbed into the bloodstream
- Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are synthesised (made) or broken down
- Enzymes are biological catalysts made from protein
- Enzymes speed up chemical reactions in cells, allowing reactions to occur at much faster speeds than they would without enzymes at relatively low temperatures (such as human body temperature)
- Substrates temporarily bind to the active site of an enzyme, which leads to a chemical reaction and the formation of a product(s) which are released
- Enzymes remain unchanged at the end of a reaction, and they work very quickly. Some enzymes can process 100s or 1000s of substrates per second
How do Enzymes work?
- Enzymes catalyse specific chemical reactions in living organisms – usually one enzyme catalyses one particular reaction:
The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
- Enzymes have specific three-dimensional shapes because they are formed from protein molecules
- Proteins are formed from chains of amino acids held together by peptide bonds
What is the Lock and Key theory?
- The ‘lock and key theory’ is one simplified model that is used to explain enzyme action
- The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit
- Enzymes and substates randomly move about in solution
- When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occur.
- A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions
What is the affect of Temperature on Enzymes?
- Enzymes work fastest at their the optimum temperature is around 37⁰C
- Heating to high temperatures (beyond the optimum) will start to break the bonds that hold the enzyme together – the enzyme will start to distort and lose its shape – this reduces the effectiveness of substrate binding to the active site reducing the activity of the enzyme
- Eventually, the shape of the active site is lost completely and the enzyme is described as being ‘denatured’
- Substrates cannot fit into denatured enzymes as the specific shape of their active site has been lost
Increasing temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
* This means that low temperatures do not denature enzymes, but at lower temperatures with less kinetic energy both enzymes and their substrates collide at a lower rate
What is the effect of pH on Enzymes?
- The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
- If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed
- This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
- Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop
How is the small intestine adapted for absorbing the products of digestion?
The small intestine has a length of around 5m this means it has a larger SA.
This interior of the small intestine is covered with millions of villi. These villi massively increase the SA.
Villi have a very good blood supply so the bloodstream rapidly removes the products of digestion. This increases the concentration gradient.
Villi also have a thin membrane.
Any molecules which cannot be absorbed by diffusion will be absorbed through active transport. MITOCHONDRIA
On the surface of villi we can find microvilli which increase the surface area even further
What is meant by chemical digestion?
- The purpose of digestion is to break down large, insoluble molecules into smaller, soluble molecules that can be absorbed into the bloodstream
- Large insoluble molecules, such as starch and proteins, are made from chains of smaller molecules which are held together by chemical bonds. These bonds need to be broken
- Enzymes are biological catalysts – they speed up chemical reactions without themselves being used up or changed in the reaction
- There are three main types of digestive enzymes – carbohydrases, proteases and lipases
What do Carbohydrase do?
Give the example of amylase
- Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch into maltose, which is then broken down into glucose by the enzyme maltase
- Amylase is made in the salivary glands, the pancreas and the small intestine
What does Protease do?
- Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine
- Protein digestion takes place in the stomach and small intestine, with proteases made in the stomach (pepsin), pancreas and small intestine
What does Lipase do?
- Lipases break down lipids (fats) to glycerol and fatty acids.
- Lipase enzymes are produced in the pancreas and secreted into the duodenum
What does Bile do?
Where is it produced?
- Cells in the liver produce bile which is then stored in the gallbladder
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Bile has two main roles:
- It is alkaline to neutralise hydrochloric acid from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
- It breaks down large drops of fat into smaller ones, increasing surface area. This is known as emulsification.
- The alkaline conditions and larger surface area allows lipase to chemically break down fat (lipids) into glycerol and fatty acids faster (the rate of fat breakdown by lipase is increased)
What is the structure of the lungs?
What happens when we inhale?
What happens when we exhale?
What is a double circulatory system?
The double circulatory system
- The human heart is part of a double circulatory system
- The circulatory system is a system of blood vessels with a pump (the heart) and valves that maintain a one-way flow of blood around the body
- The heart has four chambers separated into two halves:
- The right side of the heart pumps blood to the lungs for gas exchange (this is the pulmonary circuit)
- The left side of the heart pumps blood under high pressure to the body (this is systemic circulation)
- The benefits of a double circulatory system:
- Blood travelling through the small capillaries in the lungs loses a lot of pressure which reduces the speed at which it can flow
- By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body, meaning cells can be supplied with oxygenated blood more quickly
How is the Heart structured?
- The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right-hand side (and vice versa)
- The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs where oxygen diffuses in from the alveoli and carbon dioxide diffuses out
- The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
- Blood is pumped towards the heart in veins and away from the heart in arteries
- The chambers at the top of the heart are the atria, the chambers at the bottom the ventricles
How does the body ensure that blood only flows one way in the heart, aorta and veins?
Blood must flow one way only through the circulatory system. Valves in the heart, aorta and veins ensure this one-way flow.
Closure of a valve prevents back flow.
How does the Heart beat?
Specialised cells in the right atrium generate electrical signals that make the heart contract independently of the nervous system. These specialised cells act as a natural pacemaker.
A wave of contraction spreads across the heart - to the left atrium and then to the ventricles. This enables the ventricles to contract together.
What are the three different types of blood vessel?
- The body contains three different types of blood vessel:
- Arteries: transport blood away from the heart (usually at high pressure)
- Veins: transport blood to the heart (usually at low pressure)
- Capillaries: have thin walls which are “leaky”, allowing substances to leave the blood to reach the body’s tissues
- The walls of each type of blood vessel have a structure that relates to the function of the vessel
- Blood flows through the lumen of a blood vessel; the size of the lumen varies depending on the type of blood vessel (with arteries having a narrow lumen, and the veins a wider one)
- The lumen of the capillaries is extremely narrow, at the smallest the width of a red blood cell!
Compare Arteries and Veins?
Arteries carry High-pressure blood AWAY from the heart whereas veins carry it TOWARDSthe Heart.
Artieries carry OXYGENATED blood(exception of pulmonary artery)
while veins carry DEOXYGENATED blood with exception of the Pulmonary vein.
- *Veins** have thin walls while
- *arteries** have thick elastic muscular walls to accomodate blood.
Arteries have a small lumen while veins have a large lumen
How is CHD Caused?
In coronary heart disease (CHD), layers of fatty material build up inside the coronary arteries
- These fatty deposits are mainly formed from cholesterol; of which there are two sources in the body:
* Dietary cholesterol (from animal products eaten)
* Cholesterol synthesised by the liver
- These fatty deposits are mainly formed from cholesterol; of which there are two sources in the body:
If a coronary artery becomes partially or completely blocked by these fatty deposits, it loses its elasticity and cannot stretch to accommodate the blood which is being forced through every time the heart contracts
* This **reduces the flow of blood** through the **arteries**, resulting in a **lack of oxygen for the heart muscle**
* **Partial blockage** of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and **results in severe chest pains called** **angina**
* **Complete blockage** means cells in that area of the heart will not be able to respire aerobically, leading to a **heart attack**
* Treatment of CHD involves either increasing the width of the lumen of the coronary arteries using a stent, or prescribing statins to lower blood cholesterol
What are statins?
Statins are drugs that help to lower cholesterol in the blood. They do this by lowering its production in the liver.
Statins are prescribed for people with heart disease or who have a high risk of developing it. They need to be taken long-term. Cholesterol levels will rise again if a person stops taking them.
Statins are not suitable for everyone - they should not be prescribed for people with liver disease, or pregnant or breast feeding women.
- They block an enzyme in the liver which is needed to make cholesterol
- This slows down the rate of fatty material building up in the blood, reducing the risk of CHD occurring
- There are many advantages and disadvantages of statins:
What are Stents?
- Stents can be used to keep the coronary arteries open
- A narrow tube is threaded up through the groin up to the blocked vessel
- A tiny balloon is then inflated
- The balloon pushes the metal or plastic stent against the wall of the artery, increasing the width of the lumen
- The balloon and tube are then removed
Stents are very effective at reducing the risk of a heart attack as they widen the lumen to increase blood flow to the coronary arteries, and the procedure is relatively simple
* Stents also **last a long time,** which is a positive, however, there is a **risk of blood clots (thrombosis) occurring around** * **They do not treat the underlying disease**
What are Heart Transplants?
A heart transplant is required in cases of heart failure. Coronary heart disease can lead to heart failure. The heart fails to pump sufficient blood and organs are starved of oxygen. There are different degrees of severity of heart failure.
A transplant puts major strain on the body, and the benefits and risks will be evaluated including whether the patient’s condition is sufficiently severe and other health factors.
Artificial hearts are plastic devices used occasionally to keep patients alive whilst waiting for a heart transplant. They can also be used to allow a patient’s heart to rest to help it recover.
After the transplant, the patient will:
- There is a shortage of donor hearts in the UK.
- need time to heal, recover and build up strength
- have to take drugs called immunosuppressant drugs for the rest of their life - this prevents the person’s immune system from rejecting the donor heart
- have an increased risk of infection because of these drugs
Compare CHD treatments?
What are risk factors and give examples?
- Risk factors are linked to an increased rate of a disease; but exposure to a risk factor doesn’t guarantee that an individual will suffer a disease (a person who smokes regularly isn’t guaranteed to develop lung cancer but their risk compared to someone who doesn’t smoke is much, much higher)
- Certain risk factors correlate with certain diseases (are related to them); but correlations are not always causations
- Risk factors can be:
- Aspects of a person’s lifestyle; such as the food they eat or whether or not they drink alcohol
- Substances in the person’s body or environment; such as air pollution in a crowded city or asbestos in old buildings
Correlation and cause
If there is a correlation between a particular factor and an outcome, it does not mean that the factor necessarily causes the outcome. Scientists must look for a possible mechanism by which the factor could be the likely cause.
In the case of lung cancer, analyses of cigarette smoke have shown that at least 70 of the chemicals present in smoke will cause cancer in laboratory animals which establishes a causal link.
What are the structures in the leaf?
- The structures of plant tissues are related to their functions.
- Some important plant tissues include:
- epidermal tissues
- palisade mesophyll
- spongy mesophyll
- xylem and phloem
- meristem tissue found at the growing tips of shoots and roots
What are the adaptations of the leaves?
What is the Xylem?
Xylem
The xylem transports water and minerals from the ROOTS up the STEM and into the LEAVES.
In a mature flowering plant or tree, most of the cells that make up the xylem are specialised cells called vessels.
Vessels
- Lose their end walls so the xylem forms a continuous, hollow tube.
- Become strengthened by a chemical called lignin. The cells are no longer alive. Lignin gives strength and support to the plant. We call lignified cells wood.
Transport in the xylem is a physical process. It does not require energy.
What is the Phloem?
The phloem moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:
- growing parts of the plant for immediate use
- storage organs such as bulbs and tubers
- developing seeds.
Transport in the phloem is therefore both up and down the stem. Transport of substances in the phloem is called translocation.
Phloem consists of living cells. The cells that make up the phloem are adapted to their function:
- Sieve tubes - specialised for transport and have no nuclei. Each sieve tube has a perforated end so its cytoplasm connects one cell to the next.
- Companion cells - transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s).
How are root hair cells adapted for efficient uptake of water?
- Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport
- Root hairs are single-celled extensions of epidermis cells in the root which increase the surface area of the cells significantly; this increases the rate of the absorption of water by osmosis and mineral ions by active transport
- They grow between soil particles and absorb water and minerals from the soil
- Water enters the root hair cells by osmosis
- This happens because soil water has a higher water potential than the cytoplasm of the root hair cell
What is Transpiration?
Transpiration is the evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapour through the stomata - but does have its purposes:
- provides the water for photosynthesis
- transports mineral ions
- cools the leaf as water evaporates
- provides water that keeps the cells turgid, which supports herbaceous plants
Root hairs are single-celled extensions of epidermal cells in the root. They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Minerals enter by active transport.
Water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration
- Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
What do the stomata do?
- The role of stomata and guard cells (found predominantly on the underside of the leaf) is to control gas exchange and water loss
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When the availability of water is high, guard cells become turgid as a result of osmosis
- When guard cells are turgid, the stomata they surround are open and air can circulate in from the environment but water is consequently lost via transpiration
-
When less water is available, the guard cells lose water by osmosis and become flaccid
- When guard cells are flaccid, they pull together, closing the stomata and reducing water loss via transpiration
- Stomata are predominantly distributed on the underside of the leaf where it is cooler and shaded (lower light intensity) – this leads to less transpiration and therefore less water loss
What is Translocation?
Translocation is the movement of sugar produced in photosynthesis to all other parts of the plant for respiration and the other processes described above. This occurs in phloem cells.
