4.2 Organisation

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Define cells

The basic building blocks that make up all living organisms

Define tissue

A group of cells with a similar structure and function

They can be made up of more than one type of cell

Define organ

Organs are groups of tissues that work together to perform specific functions. They organised into organ systems

What are organ systems

Organs are organised into organ systems which work together to form organisms

What does the digestive system do and why?

The digestive system involves several organs working together to digest (break down) and absorb food.

Food eaten is large and insoluble so must be digested (broken down) into smaller soluble molecules so that it can be absorbed by cells

Define digestion

The breakdown of food from large, insoluble molecules into small soluble molecules so that they can be absorbed into the bloodstream

Define absorption

Involves the small, soluble molecules from digestion being taken into the bloodstream; they cross cell membranes in the small intestine

What are the two types of digestion?

• Mechanical

• Chemical

Define mechanical digestion and explain what it does

Physical breakdown of food into smaller pieces without changing the food’s chemical composition

It increases the surface area of the food so that enzymes can act on it more effectively during chemical digestion; it does not involve enzymes as it is a purely physical process

Give examples of mechanical digestion

• Chewing in the mouth: teeth grind and tear food

• Churning of the stomach: the stomach muscles mix and break up food

Define chemical digestion and explain what it does

Chemical digestion is the breakdown of large, insoluble food molecules into small, soluble molecules using enzymes.

It involves enzymes that chemically change the food molecules, making them small enough to be absorbed into the bloodstream through the walls (cell membrane) of the small intestine.

Give the similarities and differences between mechanical and chemical digestion

Similarities

Similarity	Explanation
Both are parts of digestion	They work together to break down food so nutrients can be absorbed.
Both occur in the mouth and stomach	Chewing (mechanical) and enzyme action (chemical) both start in the mouth; churning and enzyme activity both occur in the stomach.
Both help with absorption	Each process makes food molecules small enough for absorption in the small intestine.

Differences

Feature	Mechanical (Physical) Digestion	Chemical Digestion
What it does	Breaks food into smaller pieces	Breaks food into smaller molecules
Type of change	Physical change (no new substances made)	Chemical change (new substances formed)
Involves enzymes?	No enzymes involved	Enzymes are essential
Purpose	Increases surface area for enzymes	Converts large, insoluble molecules into small, soluble ones

What are the organs that make up the digestive system and what do they do

The digestive system is a group of organs that break down large, insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream and used by the body.
It involves mechanical digestion, chemical digestion, absorption, and excretion.

1. Mouth

Functions:

• Mechanical digestion: Teeth chew food, breaking it into smaller pieces to increase surface area for enzyme action.

• Chemical digestion: Salivary glands produce saliva containing the enzyme amylase, which starts the breakdown of starch (a carbohydrate) into maltose, a sugar.

• Saliva also lubricates food, making it easier to swallow.

2. Oesophagus

Functions:

• Transports food from the mouth to the stomach.

• The muscle contracts behind the ball of food, pushing it forward

• .No enzymes are secreted here; it’s a transport organ.

3. Stomach

Functions:

• Muscular walls churn and mix food (mechanical digestion).

• Glands in the stomach lining produce:

  • Hydrochloric acid:

    • Kills harmful microorganisms (bacteria) in food.

    • Provides an acidic pH for the protein enzymes

  • Protease enzyme:

    • Begins the chemical digestion of proteins into amino acids.

• The stomach has a thick, muscular wall to contract powerfully.

4. Liver

Functions:

• Produces bile, which has two key roles:

  1. Neutralisation: Bile is alkaline, so it neutralises the acidic chyme from the stomach to provide the alkaline conditions needed for enzymes in the small intestine.

  2. Emulsification: Bile breaks large fat droplets into smaller ones, increasing the surface area for lipase enzymes to work faster.

5. Gall Bladder

Functions:

• Stores bile made by the liver.

• Releases bile into the small intestine

6. Pancreas

Functions:

• Produces and secretes digestive enzymes into the small intestine.

• The pancreas releases pancreatic juice containing:

  • Amylase – breaks starch → maltose

  • Protease  – breaks proteins → amino acids

  • Lipase – breaks lipids (fats) → fatty acids + glycerol

7. Small Intestine

Functions:

• Completes chemical digestion using enzymes from the pancreas and the intestinal wall.

• Amylase, protease, and lipase break down all remaining food molecules:

  • Starch → glucose

  • Proteins → amino acids

  • Lipids → fatty acids + glycerol

• Absorption: The digested, soluble molecules are absorbed into the bloodstream through the villi by diffusion or active transport.

Adaptations for absorption:

• Very long length → more time for digestion and absorption.

• Villi and microvilli → massively increase surface area.

• Thin walls (one cell thick) → short diffusion distance.

• Rich blood supply → maintains a steep concentration gradient for diffusion.

• Active transport → used to absorb all glucose and amino acids even when concentrations are low.

8. Large Intestine 

Functions:

• Absorbs water from the remaining indigestible food.

• The leftover material becomes semi-solid faeces.

9. Rectum and Anus

Functions:

• Rectum: Stores faeces until it is ready to leave the body.

• Anus: Controls the removal of undigested waste (faeces)

How is the mouth adapted for its function?

• Has teeth for mechanical digestion (chewing) to break the food down into smaller pieces, giving it a larger surface area so that enzymes can act on it more effectively during chemical digestion

• Saliva contains amylase enzyme to start starch digestion

How does food move down the oesophagus?

The muscle contracts behind the ball of food, pushing it forward

How is the stomach adapted for its function?

• Muscular walls for churning (mechanical digestion)

• Produces protease enzyme

• Contains hydrochloric acid to produce an acidic environment for optimum enzyme conditions and to kill pathogens

How is the pancreas adapted for its function?

Produces (all types of) enzymes and releases them into the small intestine for digestion

How is the small intestine adapted for its function

• Many villi to increase surface area

• Many microvilli to further increase surface area

• Villi have very thin walls (one cell thick) to provide a short diffusion pathway

• Good blood supply to maintain a high concentration gradient

What are enzymes and what do they do?

Biological catalysts (substances that speed up the rate of reaction without being used up themselves); they speed up reactions by reducing the activation energy. This allows for reactions to occur at a lower temperature and a greater rate.

They breakdown large molecules into small molecules and join small molecules into large molecules

They are protein molecules and the shape of the enzyme is vital to its function because each enzymes active site is complementary to the shape of the substrate of the reaction that it catalyses

Describe the lock and key hypothesis

The shape of the enzymes active site is complementary to the shape of the substrate that it binds to. When the substrate binds to the enzyme’s active site they form an enzyme-substrate complex and the reaction takes place. The products are then released

What do enzymes require and why?

Optimum pH: if too high or too low, it will change the shape of the enzyme’s active site which causes the enzyme to be denatured

Temperature: if too low, it reduces the frequency of collisions. If too high it changes the shape of the active site causing it to become denatured

What do carbohydrases do and where are they produced?

Carbohydrases convert carbohydrates into simple sugars; one example is amylase which breaks starch into maltose

Produced in the salivary glands, pancreas and small intestine

What do proteases do and where are they produced?

Proteases convert proteins into amino acids

They are produced in the stomach, pancreas and small intestine

What are lipases and where are they produced?

They convert lipids into three molecules of fatty acids and glycerol

They are produced in the pancreas and small intestine

Where are all digestive enzymes produced?

The small intestine and pancreas

What are the products of digestion used for?

To build new carbohydrates, lipids and proteins. Some glucose is used in respiration

Where is bile produced and released and what is its function?

Bile is produced in the liver and stored in the gallbladder and released into the small intestine

It is alkaline to neutralise hydrochloric acid from the stomach so that the enzymes in the small intestine can work at the optimum pH. It also emuslifies fats to form small droplets to increase its surface area; the alkaline conditions and large surface area increase the rate of fat breakdown by lipase

What can be used to test for starch?

Iodine solution: turns from orange to blue black

What can be used to test for reducing sugars?

Benedict’s solution will turn from blue to brick red

What can be used to test for protein?

Biuret’s reagent will turn from blue to purple

What can be used to test for lipids?

Ethanol will turn a cloudy milky white

Describe the pathway protein in food will taken through the body when eaten

1. Eating and chewing (mouth)

• The food is chewed into smaller pieces by the teeth, increasing the surface area for enzymes to act on.

• No protein digestion happens here yet — just mechanical digestion

2. Swallowing and the stomach

• Food moves down the oesophagus into the stomach.

• The stomach produces protease enzymes which work in acidic conditions (because of the stomach’s hydrochloric acid).

3. Small intestine

   • The pancreas releases more protease enzymes into the small intestine.

   • These enzymes further break down the proteins into amino acids, which are small, soluble molecules.

4. Absorption

   • The amino acids are absorbed through the walls of the small intestine.

   • This happens by diffusion and active transport (depending on the current concentration of the substance in the small intestine) into the blood capillaries inside the villi

   • The villi have a good blood supply to carry amino acids away quickly, maintaining a concentration gradient.

5. Transport in the bloodstream

• Once in the bloodstream, the amino acids travel to cells all around the body.

• The cells use them to build new proteins, such as enzymes, hormones, or structural proteins (like muscle tissue).

Does active transport or diffusion take place when moving substances from the small intestine

Both diffusion and active transport take place (that is why the villi have many mictochondria) depending on the concentration of the substance in the gut at that current time.

What type of system is the human circulatory system?

It is a double circulatory system; this means that blood passes through the heart twice during one complete circuit of the body

Describe the pathway of blood throughout the circulatory system

Describe the structure of the heart and how it is adapted for its function

• Thick muscular walls so that they can contract with force to pump blood

• Left ventricle has a thicker muscular wall so that it can pump blood all around the body

• 4 chambers to separate oxygenated blood from deoxygenated blood

• Valves to prevent back flow

• Coronary arteries covering the heart to provide its own oxygenated blood supply to provide oxygen and glucose needed for it to respire to release energy for contraction

What is resting heart rate controlled by?

A group of cells in the wall of the right atrium which acts as a pacemaker

How do the group of cells in the wall of the right atrium control the natural resting heart rate?

They provide stimulation through electrical impulses which pass across the heart muscle causing it to contract

Without this, the heart would not pump fast enough to deliver the required amount of oxygen to the whole body

What can be used if an individual has an irregular resting heart rate and how does it work?

An artificial pacemaker can be used; it is an electrical device which produces electrical impulses causing the heart to contract at a regular pace

Describe the structure and function of arteries

They carry oxygenated blood away from the heart

Thick muscular walls to withstand high pressure of blood pumped from the heart

Elastic fibres which allow them to stretch when blood is pumped in and recoil to push blood forward

Narrow lumen to maintain high blood pressure to ensure fast speed of blood

No valves

Describe the structure and function of veins

Carry deoxygenated blood towards the heart

Wide lumen to reduce resistance, allowing a greater volume of blood to flow (this counteracts the low pressure flow, especially when moving against gravity)

Valves to prevent back flow

Thin walls as they don’t have to withstand high pressure

Describe the structure and function of capillaries

Capillaries exchange gas and nutrients between cells

They are one cell thick to provide a short diffusion pathway

Narrow lumen to force red blood cells to pass through in single file, pressing them against the capillary wall and further shortening the diffusion pathway

They branch to form capillary beds which are extensive networks that increase their surface area

Formula for rate of blood flow

Volume of blood / number of minutes = rate of blood flow

What is the function of the lungs?

Ventilation

Gas exchange

What are the lungs protected by?

The rib cage

What is the trachea?

The windpipe where air moves through

What are the intercostal muscles?

Muscles in between the ribs that contract and relax to expand and contract the rib cage, ventilating the lungs

What are the bronchi?

Two tubes coming from the trachea leading to the lungs. Air passes through the trachea and through each bronchi leading to each lung

What are the bronchioholes?

Smaller branching tubes that lead from the bronchi into the alveoli

What are the alveoli?

Alveoli are tiny air sacs located at the end of the bronchioles where gas exchange occurs; they are adapted for efficient diffusion of oxygen into the blood and carbon dioxide out of it

What is the diaphragm?

Large dome shaped muscle, contracting and flattening to increase the volume of the lungs and relaxing and returning to its dome shape to decrease the volume of the chest cavity

Describe the process of ventilation

During inhalation, the diaphragm contracts and flattens its dome shape to increase the volume of the lungs. This lowers the pressure of air inside of the lungs, causing air to be pulled in (as air moves from areas of high pressure to lower pressure). During exhalation, the diaphragm will then relax into a dome shape, decreasing the volume inside of the lungs and forcing the air to be pushed out.

Describe the process of gas exchange

Air will travel through the trachea, the bronchi, the bronchioles and into the alveoli. The capillaries surrounding the alveoli have a low concentration of oxygen and high concentration of carbon dioxide because the blood in the capillaries have already transported the oxygen to the body’s cells and picked up the waste carbon dioxide. Therefore the oxygen within the alveoli will diffuse into the capillaries, and the carbon dioxide within the capillaries will diffuse into the alveoli.

Describe how the trachea and bronchi are adapted for their function

The trachea has cartilage to keep it open

The trachea and bronchi have cillia and the mucus to trap dust and pathogens

Describe how alveoli are adapted for gas exchange

Many alveoli provide a large surface area, allowing more gas to diffuse at once

The alveolus wall and the capillary wall and are only one cell thick, providing a short diffusion pathway

The alveoli are surrounded by a network of capillaries, providing a high blood supply which maintains a steep concentration gradient

The walls of the alveoli are permeable, allowing gases to move freely in and out

What is blood?

A tissue consisting of plasma, in which red blood cells, white blood cells and platelets are suspended

What is plasma?

The liquid that carries the components in blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies and antitoxins

What are red blood cells?

They are specialised blood cells which carry oxygen from the lungs to the body’s tissues and carry carbon dioxide back to the lungs to be exhaled

Describe the structure and adaptations of a red blood cell

They contain the red pigment haemoglobin; this red pigment binds to oxygen forming oxyhaemoglobin, allowing them to carry oxygen efficiently

They have no nucleus, allowing more space for haemoglobin so each cell can carry more oxygen

Bioconcave disc shape, increasing their surface area so they can carry more oxygen

They are small and flexible, allowing them to squeeze through narrow capillaries to reach all tissues

What are white blood cells?

They are a specialised type of blood cells that is a part of the body’s immune system; their main role is to defend the body against pathogens which cause disease.

Describe the structure and adaptations of a white blood cell

They can change their shape to perform phagocytosis and to squeeze through capillary walls to move through tissues

They have a nucleus which contains DNA needed to control their complex functions and make proteins like antibodies and antitoxins

Describe the two types of white blood cells and their functions

Phagocytes: they engulf and digest pathogens in a process called phagocytosis to destroy the pathogens

Lymphocytes: these cells produce antibodies that stick to pathogens and destroy them, and produce antitoxins to neutralise toxins produced by bacteria

What are platelets and what is their function

Tiny fragments of cells which help to clot blood at the site of a wound

The clot dries and hardens to form a scab, allowing new skin to grow underneath preventing excessive bleeding and microorganisms from entering

They have no nucleus to provide more space for chemicals needed in the clotting process

Which blood cells have/ don’t have nuclei?

White blood cells have nuclei

Red blood cells don’t to provide space for haemoglobin

Platelets don’t to provide space for chemicals needed in the clotting process

What is meant by the term non communicable disease?

A disease that is not infectious and are caused by lifestyle and genetic factors

What is coronary heart disease and describe its implications

A non communicable disease caused by the build up of fatty material within the coronary arteries, narrowing them. This reduces the blood flow through the coronary arteries, resulting in a lack of oxygen and glucose for the heart muscle, meaning that the heart cannot respire efficiently. This may cause the heart to have to respire anaerobically, meaning that lactic acid may build up causing the muscle tissue to become acidic, leading to pain (angina). The acidity and lack of energy can cause damage to the cells causing them to stop working or die, leading to a heart attack. The heart may also beat irregularly or weaken, reducing blood flow to the rest of the body.

If a coronary artery becomes completely blocked, that part of the heart muscle is starved of oxygen and can die, causing a heart attack.

Name the treatments of coronary heart disease

• Stents

• Statins

• Heart transplants

  • Mechanical

  • Biological

Describe the advantages and disadvantages of the treatments of coronary heart disease

CHD is a disease that occurs when fatty deposits (plaques) build up inside of the coronary arteries, reducing blood flow and therefore oxygen and glucose supply to the heart

1. Stents

What they are:
A stent is a small metal mesh tube inserted into a narrowed artery to keep it open, allowing blood to flow normally.

Advantages	Disadvantages
Keeps arteries open so oxygen and glucose can reach the heart muscle.	Risk of blood clots forming near the stent
Long-term effect — works for many years.	Surgery carries some risks, e.g. infection or damage to the artery.
Quick recovery time compared to major surgery.	Arteries can narrow again over time if lifestyle changes aren’t made.

2. Statins

What they are:
Statins are drugs that lower blood cholesterol levels, slowing down the build-up of fatty deposits in arteries.

Advantages	Disadvantages
Reduce risk of heart attack and stroke.	Must be taken regularly for life.
Reduce levels of bad cholesterol (LDL) in the blood which reduces risk of fatty deposits building up	May cause side effects like muscle pain, liver damage, or tiredness.
Increases levels of good cholesterol (HDL) which remove bad cholesterol (LDL) circulating in the blood	Takes time to have an effect — doesn’t treat blockages already there.

3. Heart transplants

Mechanical transplant

Advantages	Disadvantages
Keeps the patient alive while waiting for a heart transplant.	Surgery is risky and can lead to bleeding or infection.
Can pump blood effectively if the natural heart stops working.	Blood clots can form, increasing risk of stroke.
No need for a donor immediately.	The patient must take drugs to thin the blood, which can cause excessive bleeding.
Reduces risk of organ rejection (it’s not living tissue).	Bulky and expensive, and parts can wear out or fail.

Biological transplant

Advantages	Disadvantages
Can restore full heart function and give a long-term solution.	Requires a suitable donor, which can take a long time.
Improves quality and length of life if successful.	Major surgery — long recovery time and risk of complications.
No need for long-term mechanical support.	Risk of organ rejection — the immune system may attack the new heart.
—	Patients must take immunosuppressant drugs for life, increasing risk of infection.

Describe the advantages and disadvantages of treatments of faulty valves

If a valve becomes faulty (leaky or stiff and won’t open), blood flow is reduced or may flow in the wrong direction, decreasing the heart’s efficiency and therefore forcing the heart to work harder.

1. Mechanical (Artificial) Valves

Made of: Strong materials like metal or carbon.
Function: Last a long time and control blood flow effectively.

Advantages	Disadvantages
Longer lasting, more durable, don’t wear out as easily, less likely to need replacing	Blood clots are likely to form on the valve; patients must take blood thinning medication for life
No risk of tissue rejection	As medication thins bloods, can lead to excessive bleeding after injury
	Can hear the valves opening and closing

2. Biological (Natural) Valves

Made from: Animal tissue (e.g. pigs or cows) or human donors.
Function: Act just like natural valves.

Advantages	Disadvantages
No need for lifelong blood thinning medication; as they are less likely to cause blood clots	Need replacing as they degrade over time
Quiet/ don’t hear them clicking	Risk of rejection; Immune system identifies the foreign cells and initiates an immune response
	More likely to need further operation/ replacement valves; valves may harden Ethical issues; animals

Both valves are readily available, little wait time

Describe the advantages and disadvantages of treatments for heart failure

Heart failure means that blood cannot be pumped around the body

1. Mechanical / Artificial Heart

Advantages	Disadvantages
Keeps the patient alive while waiting for a heart transplant.	Surgery is risky and can lead to bleeding or infection.
Can pump blood effectively if the natural heart stops working.	Blood clots can form around the metal, increasing risk of stroke.
No need for a donor immediately.	The patient must take drugs to thin the blood, which can cause excessive bleeding.
Man made, so are less likely to be immunologically rejected	Bulky and expensive, and parts can wear out or fail.

2. Heart Transplant (from a donor)

Advantages	Disadvantages
Can restore full heart function and give a long-term solution.	Requires a suitable donor, which can take a long time.
Less risky and more natural than artificial hearts	Risk of organ rejection — the immune system may attack the new heart.
No need for long-term mechanical support.	Patients must take immunosuppressant drugs for life, increasing risk of other infection.

Give the advantages and disadvantages of treatment for blood loss?

Treatment	Description	Advantages	Disadvantages
Blood Transfusion	Donated blood from a matching donor replaces lost blood.	• Restores blood volume quickly. • Replaces red blood cells → normal oxygen transport. • Can be lifesaving after severe blood loss.	• Risk of infection (though low). • Risk of immune reaction if blood types don’t match. • Limited supply of donor blood. • Requires time for cross-matching and storage.
Artificial Blood (Blood Substitutes)	A sterile solution (e.g. saline or oxygen-carrying fluid) used to replace lost blood volume temporarily.	• Maintains blood pressure and circulation. • No need for blood type matching. • No risk of disease transmission. • Can be stored for long periods and used in emergencies.	• Most types do not carry oxygen effectively. • Only a temporary fix until real blood is available. • Some types may cause side effects.

Define health

Health is the state of complete emotional, physical and social wellbeing and not merely the absence of disease or infirmity

Describe what is meant by a communicable disease

A disease that can be transmitted from one organism to another (infectious/ transmissible)

Describe what is meant by a non communicable disease

A disease that cannot be transmitted from one organism to another

Give factors that can affect health

Diet

Stress

Lifestyle

Drug usage

Physical activity

Life situation (access to healthcare, education)

What is meant by a risk factor

Factors that are linked to an increase in the likelihood that someone will develop a disease in their lifetime, but do not guarantee that someone will get this disease

True or false: risk factors do not directly cause disease

False.

Some risk factors directly cause disease, some do not.

What is cancer?

Changes in cells that lead to uncontrolled growth and cell division

What is a tumour?

An abnormal mass of cells (tissue) formed when cells grow and divide more than they should, or not die when they should - usually forms due to uncontrolled cell division.

Name and define the two types of tumours

Benign: growths of abnormal cells which are contained in one area (usually within one membrane) that do not invade other parts of the body. This tumour is not cancerous.

Malignant: these tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body by travelling through the bloodstream where they form secondary tumours.

What are the two types of risk factors for cancer?

Lifestyle and genetic

Name the plant organs

Roots, stems, leaves, flowers, fruits.

These organs work together to form an organ system that allows for transport of substances and other vital functions.

What is the purpose of the plant organs?

To form an organ system for the transport of substances around the plant

What are plant organs made up of and why?

They are made up of plant tissues, made up of specialised cells with specific functions that allow the plant to carry out their functions

Name the plant tissues and briefly describe their functions

Epidermal tissue (covers the whole plant)

Palisade mesophyll tissue (where most photosynthesis happens)

Spongy mesophyll tissue (contains large air spaces to allow air to diffuse into and out of the cell)

Xylem tissue (transports water and mineral ions through the roots, stems and leaves, through the process of transpiration)

Phloem tissue (transports sugars, amino acids, hormones and other dissolved substances produces in photosynthesis from the leaves to the rest of the plant, through the process of translocation)

Meristem tissue (found at the tips of the roots and shoots of plants and is able to differentiate into many different types of plants cells, allowing it to grow)

What tissues does the leaf have?

Epidermal tissue

Palisade mesophyll tissue

Spongy mesophyll tissue

Xylem tissue

Phloem tissue

Describe how the epidermal tissues’ structure is related to its function

• Covered by a hydrophobic waxy cuticle: this prevents water loss through evaporation, but is transparent so still allows light to pass through to photosynthetic cells; also acts as a defence mechanism, acting as a protective outer barrier to prevent the entrance of pathogens into the plant

• Upper epidermis is transparent, allowing light to pass through to the palisade mesophyll

• Lower epidermis has many stomata allowing gases to diffuse into and out of the organ (for has exchange)

• Guard cells control the size of the stomata by changing shape, to control gas exchange and the rate of water loss (responding to environmental conditions)

Describe how the palisade mesophyll's structure is related to its function

• Closely packed and full of chloroplasts to maximise the amount of light that can be absorbed for photosynthesis

• Near the top of the leaf, so that they can get the most light

Describe how the spongy mesophyll’s structure is related to its function

• Many air spaces between cells to allow for gas exchange and for gases to move through the mesophyll layer to reach all cells

Describe how the xylem and phloem structure is related to its function

• They are grouped together in vascular bundles allowing substances to be transported efficiently throughout the plant

• The vascular bundles form a continuous network

• Being bundled together, the delicate phloem tissue is protected (as it is on the inner bit)

• Xylem’s thick, lignified walls provides structure for the plant and strengthens the stem to allow it to stay upright

Describe how phloem is adapted for its function

Function: to transport sugars, amino acids, hormones and other dissolved substances made in photosynthesis from the leaves to the rest of the plant in the process of translocation (which requires energy as it transports substances in any direction)

• Have sieve plates which are perforated with pores to allow substances to move between cells in both directions

• Has very few organelles, allowing more space for the movement of substances

• The elongated phloem cells are alive, unlike xylem, to allow them to respire to release energy needed for translocation

• Bidirectional transport, to supply all parts of the plant with energy for growth and for storage tissues

• Each sieve tube element has a companion cell next to it which respire to release energy for translocation for the phloem

Why does the phloem transport sugar?

For immediate use (respiration for energy etc.)

Storage

Describe how xylem is adapted to its function

Function: transports water and mineral ions from the roots through to the leaves and provides structural support for the plant

• Are dead cells so have no organelles allowing more space for water to move through the tubes.

• As they are dead, they also have no end walls, forming a continuous hollow tube making it easier for water to flow freely with no resistance

• Cell walls are strengthened with lingin, making them strong and waterproof so they do not collapse under the pressure of water movement

Describe how root hair cells are adapted to their function

Function: take up water by omosis and mineral ions by active transport

• Long hair-like extensions to increase surface area

• Thin cell wall to provide a short diffusion pathway

• Large vacuole to maintain a steep concentration gradient (contains a great concentration of cell sap (solute) and a low concentration of water, keeping a low water potential for the cell)

• Many mitochondria for respiration to release energy needed for active transport to move mineral ions into the cell

Describe how guard cells work

Guard cells change shape to reduce and increase the size of the stomata. When the plant has lots of water, the guard cells fill with this water to go plump and turgid.This causes the stomata to become more open, allowing more gases to diffuse into the leaf for more photosynthesis.

When the plant has less water, the guard cells will also lose water and become flaccid, causing the stomata to decrease in size. This then prevents the rate of water loss by stopping too much water vapour from escaping.

Guard cells are also sensitive to light, so at night will close to reduce water loss when there is no photosynthesis taking place.

Therefore guard cells are adapted for gas exchange and controlling water loss within a leaf.

Define transpiration

Transpiration is the loss of water vapour (through evaporation) from the leaves of the plant through the stomata.

Describe how transpiration creates a transpiration stream

Transpiration stream: The transpiration stream is the continuous upward movement of water from a plant's roots to its leaves.

As water vapour evaporates out of the leaves of the plant through the stomata, it creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. (The evaporation of water creates a pull that causes the transpiration stream).

This in turn means that more water is drawn up from the roots, and so there is a constant transpiration stream of water through the plant.

Transpiration is just a side effect of the way that leaves are adapted for photosynthesis; the purpose of stomata is to allow gases to diffuse into and out of the plant to be exchanged easily, however because there is more water in the plant than outside of the plant, the water escapes from the leaves through the stomata by diffusion.

Describe the four factors that affect the rate of transpiration and how they impact it

Four factors: humidity, light intensity, temperature, air flow

• Greater light intensity = greater rate of transpiration: In bright light, stomata open to let in more carbon dioxide for more photosynthesis. This allows more water vapour to escape, increasing transpiration. In darkness, stomata close, so transpiration slows.

• Greater temperature = greater rate of transpiration: Warmer air gives water molecules more kinetic energy, so evaporation from leaf cells and diffusion of water vapour out of the leaf happen faster.

• Greater humidity = lower rate of transpiration: When the air is humid, it already contains a lot of water vapour, so there’s a smaller concentration gradient between the inside and outside of the leaf — less water diffuses out.

• Greater wind speed = greater rate of transpiation: Wind blows away water vapour around the leaf surface, maintaining a steep concentration gradient, so water continues to diffuse out quickly. Still air allows moisture to build up, slowing transpiration.

Why may two plants kept in the same conditions have different rates of transpiration

Plant with the faster rate of transpiration

• More stomata:

  • Bigger leaves

  • More leaves

  • Greater total surface area of leaves

• Less amounts of waxy cuticle

Explain why having only one ventricle makes the circulatory system less efficient than having two ventricles.

oxygenated and deoxygenated blood mixes

(so) less oxygen reaches the body / tissues / cells