Module Two : 5. Nutrient and gas requirements

Answer 1

Autotroph Structure and Function in Plants

Vascular Plants and Their Transport System
* Most plants are vascular plants due to their transport system for moving substances.
* Non-vascular plants, like mosses and liverworts, have a simple structure where nutrients are absorbed and wastes removed through diffusion and osmosis.

Tissues in Plants
* Plants have specialized cells grouped together into tissues, such as photosynthetic tissue.
* These tissues form organs that carry out specific functions within the plant, including transport of substances, photosynthesis, reproduction, and gas exchange.

Vascular Plants’ Body Systems
* The root, shoot, and vascular system are the body systems found in plants.
* Each system has specialized organs to carry out specific functions.
* The two types of vascular tissue are xylem and phloem.

Root System Functions
* The root system anchors the plant and absorbs water and inorganic nutrients from the soil.
* The roots have a large surface area that allows efficient absorption of water and mineral salts.
* The root hair zone is in the younger part of each root, near the tip, where the epidermal cells protrude outwards into the surrounding soil.
* Water moves into the roots by osmosis, while mineral ions usually move into the roots by diffusion.

Stems and Leaves in the Shoot System
* The stem provides both structural support and a transport pathway between the roots and the leaves.
* The stem contains dermal tissue, vascular tissue, and ground tissue.
* The arrangement of vascular tissues varies between different plant species.
* Ground tissue in the stem fills in around the vascular tissue.

Answer 2

Plant Shoot System Overview

Absorption of Sunlight and Carbon Dioxide
* Leaves absorb sunlight and carbon dioxide to produce glucose in photosynthesis.
* The thin, flat structure of leaves allows maximum absorption of light energy by chlorophyll inside the cells.
* The outermost layer of cells, the epidermis, is transparent, allowing sunlight to penetrate to the photosynthetic cells.

Mesophyll Cells
* The mesophyll, or middle layers of the leaf, is responsible for most of the plant’s photosynthesis.
* Two main types of cells make up the mesophyll: palisade cells and spongy cells.
* In hot, dry habitats, plants risk losing a lot of water through evaporation.
* In hot, dry environments, plants have copious amounts of sunlight but high rates of evaporation of water.

Gaseous Exchange
* The epidermis covers the surface of leaves, protecting the delicate inner tissues and secreting a waterproof cuticle.
* Guard cells control the exchange of gases (such as carbon dioxide and oxygen) and the loss of water through leaves.

Transport
* The vascular tissue in the centre of the root is continuous, passing up the stem and into the leaves as’veins’ in the leaf.
* The distribution of vascular tissue throughout the leaf ensures no leaf cells are too far away from a transport source.

Cellular Respiration in Plants
* Plants carry out cellular respiration as well as photosynthesis.
* During the day, the oxygen required for cellular respiration comes from the oxygen produced as a by-product of photosynthesis.
* The carbon dioxide released as a result of cellular respiration during the day is used as a reactant in photosynthesis.

Imaging Technologies Used to Determine Plant Structure
* The development of advanced technologies has led to a greater understanding of plant structure and functioning.
* Advanced computer modelling has facilitated the capture, manipulation, and processing of images, enabling the production of a three-dimensional (3D) image of a plant.

Answer 3

Plant Structure Study through MRI and Micro-CT

• MRI uses radio waves and a magnetic field to create a 3D image of plant structures.
• MRI is particularly useful for studying roots in clear containers.
• MRI images can be combined with PET or NT images for functional information about transport and processes.
• X-ray computed microtomography (micro-CT) is an emerging technology for understanding plant internal structure.
• Micro-CT is non-destructive, similar to CT scans in hospitals, but on a smaller scale and with higher resolution.
• X-ray beam rotation records hundreds of images from different angles, which are analyzed and reconstructed into a 3D image.

Answer 4

Photosynthesis Tracing and Isotopes

• Photosynthesis is a process where sunlight acts on carbon dioxide to initiate the manufacturing of organic compounds.
• Melvin Calvin used a radioactive tracer, carbon-14, to show sunlight acts on chlorophyll, revealing the origin of organic compounds.
• Radioisotopes, different forms of the same element, emit radiation to achieve a stable state.
• Radioisotopes are useful as tracers in physical, chemical, and biological systems.
• They were used to determine whether the oxygen released during photosynthesis originated from water or carbon dioxide.
• Carbon-14, added to a plant’s carbon dioxide supply, is incorporated into the glucose molecules produced during photosynthesis.
• The pathway of glucose movement can be traced using the radiation emitted by the carbon-14 and recorded in an autoradiograph.
• Modern computer software can convert this information into 3D images to visualize the movement of radioactively labeled chemicals in living organisms.
• Real-time radioactive imaging system (RRIS) and PlanTIS are used to trace the movement of carbon-11, incorporated into the glucose molecule.

Answer 5

Photosynthesis Tracers and Technologies
* Radioisotopes emit radiation, used as tracers in photosynthesis.
* Used to confirm oxygen in photosynthesis comes from water, not carbon dioxide.
* Carbon-14 added to carbon dioxide traced glucose movement in plants.
* New technologies enable 3D images of photosynthesis product structures and pathways.

Answer 6

Gas Exchange in Organisms and Animals

Gas Exchange in Organisms
* Gas exchange is crucial for all living cells, requiring a constant supply of oxygen and removal of carbon dioxide.
* Both plants and animals have specialized structures for efficient gas movement.
* The respiratory surface is the surface that gases cross, and the movement of these gases is by diffusion.
* In unicellular organisms or small multicellular organisms, the movement of substances occurs across the entire cell membrane or the thin body wall.
* Large multicellular organisms require specialized structures and systems to ensure the efficient movement of these gases.

Gas Exchange in Plants
* Leaves are well adapted for gaseous exchange, with large, flat leaves and moist surfaces.
* Stomata, or pores in the epidermis, allow gases to move into and out of the plant.
* Stomata are bordered by two bean-shaped guard cells, which contain chloroplasts.
* Stomata open and close to allow gas diffusion, but when they are closed, no gases are transported and no water is lost.
* The opening and closing of stomata depend on several environmental factors, including light, temperature, and the concentration of carbon dioxide inside the leaf.

Gas Exchange in Animals
* Gas exchange occurs in all animals, involving the movement of gases between the internal and external environments by diffusion across cell membranes.
* Oxygen is essential for all cells to carry out cellular respiration, and carbon dioxide is produced and must be removed.
* The respiratory system enables the exchange of gases between an organism and its environment.
* In microscopic organisms, gas exchange occurs by diffusion across their cell membrane. In larger terrestrial animals, the gas exchange system is inside the body to prevent dehydration of the gas exchange surfaces.

Answer 7

Mammalian Digestive System Overview

• Mammalian heterotrophs need to consume all their nutrient requirements to supply energy and organic compounds.
• The digestive system breaks down complex food into simpler molecules that can be absorbed into the bloodstream.
• Two types of digestion: mechanical and chemical.
• Mechanical digestion involves the physical breakdown of food particles by teeth and stomach churning.
• Chemical digestion uses digestive enzymes to break down large, complex molecules into smaller, simpler forms.
• Simple substances obtained include glucose from complex carbohydrates, amino acids from proteins, glycerol and fatty acids from lipids, and nucleotides from nucleic acids.

Pathway through the Digestive System

• Mechanical digestion begins in the mouth with salivary amylase, which breaks down complex carbohydrate starch into simpler sugars.
• The bolus is swallowed and enters the oesophagus, where it travels along the soft-walled, muscle-ringed tube to the stomach.
• The stomach has narrow openings controlled by circular sphincter muscles, allowing mechanical digestion.
• The bolus breaks up into pieces that combine with gastric juices to form a mixture known as chyme.
• The enzyme pepsinogen converts into an active form called pepsin in the acidic environment, breaking down long-chained proteins into shorter chained peptides and nucleic acids into their component nucleotides.
• The chyme remains in the stomach for about 6 hours.
• The small intestine contains the duodenum, jejunum, and ileum, with the chyme entering the duodenum stimulated by a hormone.
• Bile is released into the duodenum when there are lipids present in the chyme, breaking down fats into smaller pieces or fat droplets.
• Food enters the jejunum where most of the absorption of the digestive products occurs.
• The products of digestion move into the body’s transport systems in the small intestine through tiny projections called villi, which are moist and one cell thick.

Answer 7

Understanding the Digestive System and Its Functions

The Liver and Small Intestinal Regions
* The liver is the center of food metabolism, maintaining balance in sugars, glycogen, and protein levels.
* The small intestine, consisting of the duodenum, jejunum, and ileum, is responsible for most digestion.
* The pancreas releases digestive enzymes and bicarbonate ions, which neutralize the acidic chyme.
* The liver’s bile, stored in the gall bladder, emulsifies fat molecules for breakdown by lipases.
* Other enzymes complete the chemical breakdown of larger molecules.

The Large Intestinal Regions
* The large intestine, composed of water, salts, and dietary fiber, moves the remaining undigested material to the large intestine.
* The colon absorbs water and some salts back into the bloodstream, while vitamins A and K are absorbed into the bloodstream.
* The remaining waste material, faeces, is moved into the rectum by peristalsis and egested from the body through the anus.

The Fate of Digestive Products
* The end products of digestion can be built up into useful substances, either as new biological material or an energy source.
* In mammals, blood transports the products of digestion to where they are needed in the body.
* The end products can be reassembled into structural parts or into energy storage.

Comparing Nutrient and Gas Requirements
* Autotrophs and heterotrophs have different methods of obtaining their nutrient and gas requirements.
* Autotrophs carry out photosynthesis, using the energy from the sun into high-energy bonds in glucose molecules.
* Autotrophs also require oxygen gas for cellular respiration and can convert some of the glucose they produce into other organic compounds.

Answer 7

Plant Transport Systems and Function

Xylem and Phloem Tissues
* Xylem tissue carries water and mineral ions in one direction from roots to leaves.
* Phloem tissue transports sugars and other photosynthesis products from leaves to the rest of the plant.
* Xylem vessels are long, thin, continuous tubes composed of dead tissue with lignin-strengthened walls.
* The transpiration-cohesion-tension theory explains the movement of substances up the xylem vessels.

Phloem Cells
* Two types of phloem cells: sieve tube cells and companion cells.
* Sieve tube cells are long, thin phloem cells with large pores through the cell walls at either end.
* Companion cells are found alongside the sieve tubes, providing ATP and nutrients and assisting the loading and unloading of sugars into the sieve tube cells.

Source-Sink Theory
* After glucose is produced in the leaves in photosynthesis, it is either stored as starch or converted to sucrose and distributed to all parts of the plant.
* Substances transported in the phloem move in whichever direction is required.
* Up to 90% of the dissolved substances in the sap of the phloem is sucrose.
* The driving force for the movement of substances is caused by the formation of high- and low-pressure regions within the phloem tissue.

Hypotheses, Theories, and Models about Plant Function
* Scientists have a deep knowledge about the structure and function of plants and the processes that occur in them.
* The process of photosynthesis began with experiments carried out in the 17th century to determine whether plants ‘ate the soil’ to grow.

Answer 7

Respiratory Systems in Animals and Other Animals

Respiratory Systems in Animals
* Animals have internal respiratory systems to reduce water loss.
* The gaseous exchange surfaces in mammals are located in the lungs, known as alveoli.
* The alveoli are composed of an air sac connected to the external environment and surrounded by tiny blood vessels called capillaries.
* The movement of gases between the air in the alveoli and the bloodstream occurs by diffusion across a concentration gradient.
* Oxygen in the incoming alveolar air is in a higher concentration than in the bloodstream, so oxygen diffuses from the air sacs into the bloodstream.
* Carbon dioxide is more concentrated in the capillary and diffuses out into the alveolar space.

Respiratory Systems in Other Animals
* Fish have specialized structures called gills to absorb the small amount of oxygen that is dissolved in water.
* Insects take in and expel air through structures called spiracles, which are in effect breathing pores.
* The respiratory surface in insects differs from all other internal respiratory systems in that it has no blood or blood capillaries involved in the transport of gases.
* The number of open and closed spiracles generally controls the rate of respiration in insects.
* Insects exchange gases via pores called spiracles, which lead to tracheal tubes, which then branch into smaller tubes called tracheoles.

Answer 8

Transport Systems in Multicellular Organisms

• Unicellular and simple multicellular organisms obtain nutrients and waste through diffusion, osmosis, and active transport.
• Transport systems in plants and animals ensure efficient and effective cell function by moving substances around the organism.
• Transport systems in plants and animals contain a system of vessels for transporting substances, a suitable transport medium (fluid), and a driving mechanism.
• Differences between transport systems in plants and animals are found in the type of structures and components, the substances transported, and the mechanisms driving these substances’ movement.
• Xylem tissue in plants transports water and mineral ions from roots to leaves, while phloem tissue transports photosynthesis products to all plant regions.
• Xylem tissue consists of xylem tracheids and xylem vessels, with other cells such as parenchyma and fibres in between.

Xylem Transport in Plants: Transpiration-Cohesion-Tension Theory

• Xylem vessels in flowering plants form continuous tubes for water transport.
• Cell walls break down when cells specialize to become xylem vessels, leaving hollow vessels for easy water and mineral ion flow.
• Xylem vessels and tracheids are reinforced with lignin thickenings to prevent vessel collapse and facilitate water and dissolved substance movement.
• Fibers support the xylem tissue, and parenchyma tissue facilitates material movement and storage.
• The transpiration-cohesion-tension theory explains the upward movement of materials in the xylem.
• The theory explains the evaporation of water from leaves, creating a suction pull of water up the stem from the roots, known as the transpiration stream.
• The movement of this column of water from the roots is aided by the cohesion of water molecules, adhesive forces between water molecules and xylem vessel walls, and the narrow, thickened, lignified walls of the xylem vessel.
• Once water and mineral ions are absorbed into the roots, they move across the root into the xylem, causing a small amount of root pressure to force the solution already present in the xylem to move upwards.
• Transport systems in plants carry water and mineral ions in one direction only, from the roots to the leaves, in the xylem tissue.

Answer 9

Heterotrophic and Autotrophic Nutrition

• Heterotrophs do not require carbon dioxide for photosynthesis, but need to consume glucose and other organic compounds.
• Heterotrophs require oxygen for cellular respiration and energy production.
• Both types of nutrients require inorganic and organic substances, water, and oxygen gas.
• Autotrophs produce their own organic nutrients using sun energy, but need to obtain inorganic substances like water, mineral ions, and gases like carbon dioxide and oxygen.
• Autotrophs manufacture their own glucose and other organic substances from inorganic nutrients.
• Heterotrophs must obtain all their organic nutrients by consuming autotrophs or other heterotrophs.

Answer 10

Photosynthesis: The Evolution of Plants and Their Role in Life

Jan Baptista van Helmont’s Experiment
* Van Helmont believed soil formed all plant matter.
* He weighed 90 kg of dried soil and planted a willow seedling.
* The soil weighed 89.9 kg, while the plant weighed 76.1 kg.
* Van Helmont concluded that all plant matter came from water, but his experiment was flawed.
* He did not include the mass of lost leaves in his measurements, had no control to test if only water was used, and only tested one plant.

Joseph Priestley’s Experiment
* Priestley observed that a mint plant in an enclosed space could restore air after a candle or mouse died.
* He concluded that plant growth replaced the factors removed by the candle and mouse.
* Priestley’s experiments contributed significantly to the understanding of photosynthesis.

Jan Ingenhousz’s Experiment
* Ingenhousz set up a similar experiment with a candle and plant in a bell jar.
* He submerged a small aquatic plant in water exposed to light and then subjected it to darkness.
* Ingenhousz showed that light is necessary for plants to make oxygen and that bubbles formed around the leaves and green parts of the stem when exposed to light.
* Ingenhousz is credited with discovering photosynthesis.

Ongoing Investigations
* Experiments and results are used as a basis for further investigation.
* Hypotheses, theories, and models are sometimes changed in response to results of subsequent experiments.

Understanding Plant Structure and Functioning
* Scientists have developed a comprehensive understanding of plant structure and function.
* Hypotheses, theories, and models are continually updated based on new information and results.
* Many scientists have contributed to the understanding of photosynthesis and the transpiration-cohesion-tension theory.

Transport Systems in Animals
* Multicellular organisms require a constant supply of nutrients and oxygen, and the removal of waste products.
* Two types of transport systems are open and closed.
* Open circulatory systems are composed of one or more hearts and open-ended blood vessels.
* They are not sealed and exchange only nutrients and wastes with cells.
* The transport fluid in an open circulatory system is called haemolymph, a mixture of blood and tissue fluid.
* The transport fluid flows into the sinuses in the body cavity, bathing cells directly.

Closed Circulatory Systems
* Found in all vertebrate animals, these systems transport nutrients and oxygen to all cells and carry wastes away from cells.
* The main transport system is the cardiovascular system, which moves blood in the correct direction through a series of vessels.
* A closed transport system is like a system of roads where useful substances are taken to the houses, and wastes are removed from these houses via the system of roads.

Answer 11

Understanding the Heart and Blood System in Animals

Heart Types and Blood Flow
* The heart can be two-chambered, three-chambered, or four-chambered.
* Blood flows through veins, arteries, and capillaries.
* The exchange of nutrients, wastes, and gases occurs between blood and fluid surrounding cells.
* Capillaries form a link between arteries and veins, allowing no cell to be far from a capillary.

Closed Circulatory Systems
* The muscular heart pumps blood under high pressure for efficient transport.
* A four-chambered heart is the most efficient pumping mechanism.
* Open circulatory systems contain a heart that contracts and pushes haemolymph through vessels to bathe organs.
* Closed circulatory systems contain blood enclosed in vessels, with a heart providing the driving force.

Lymphatic System
* The lymphatic system forms part of the transport system in mammals.
* The fluid surrounding cells diffuses out of the capillaries as they pass through the tissues.
* Lymph vessels in the tissues absorb this fluid, along with other substances, to prevent it from building up in the tissues.
* Lymphatic vessels from all regions of the body join up to form two main lymphatic channels.

Blood as a Medium of Transport
* Blood is the fluid transport medium that flows through the heart and blood vessels of the cardiovascular system in vertebrates.
* Human blood usually has a temperature of 38°C and a pH of 7.35.
* The volume of blood in the human body varies slightly from one person to the next, but an adult human has approximately 5 litres of blood.

Blood Function and Structure

Red Blood Cells
* Mainly transport oxygen, with approximately 4–6 million per millilitre of blood.
* Form in bone marrow, with a nucleus that disintegrates as the cell matures.
* A red pigment called haemoglobin develops inside the cell, allowing more oxygen carrier.
* Small, round, biconcave, and slightly flattened, they can squeeze through narrow capillaries.
* Life expectancy is approximately 4 months, with replacement by newly formed blood cells.

White Blood Cells
* Also produced in bone marrow, play a part of the immune system, defending the body against foreign bodies.
* There are approximately 4000–11,000 white blood cells per mL of human blood.
* Types vary in lifespan and function, with some living for a few minutes to days and others for years.
* Larger than red blood cells, not as abundant, and all have a nucleus.

Platelets
* crescent-shaped, half the size of red blood cells, produced in the bone marrow.
* Function in blood clotting by sticking to each other and developing wound fibres.
* Contact between fibres and platelets releases an enzyme, thromboplastin, to seal blood vessels and prevent excessive blood loss.

Answer 12

Understanding Blood Transport and Structure

Blood Clots and Plasma
* Plasma, the yellow, watery fluid part of blood, carries many substances in either dissolved or suspended form.
* It carries plasma proteins, nutrients, gases, excretory waste products, ions, regulatory substances, and vitamins.

Transport Systems in Mammals
* The cardiovascular system transports excess tissue fluid back to the cardiovascular system.
* The cardiovascular system consists of blood, the heart, and blood vessels.
* Blood is composed of 55% plasma and 45% blood cells (red, white, and platelets).
* Red blood cells have no nucleus, have a biconcave shape, and contain haemoglobin, which carries oxygen.
* White blood cells contain a nucleus and play a role in defense of the body.
* Platelets have a tiny, crescent shape and play a key role in blood clotting.

Blood Vessels
* Arteries carry blood away from the heart, veins carry blood back to the heart, and capillaries form a network to reach all cells in the body.
* Arteries have thicker walls to cope with the pressure of pulsing blood.
* Veins carry blood back to the heart, with thinner walls and valves to ensure blood moves in only one direction.
* Capillaries have thin walls to allow for efficient diffusion of substances and an internal diameter slightly larger than the diameter of red blood cells.

The three types of blood vessels are arteries, capillaries, and veins. Arteries carry blood away from the heart, veins carry blood back to the heart, capillaries form networks for all cells, and capillary walls are one cell thick for easy exchange between blood and cells.

Answer 13

Understanding the Heart and its Functions

Heart Function and Composition
* The heart is the driving force in the circulatory system of animals.
* It has a four-chambered heart with two chambers: the atria (top chamber) and the ventricles (bottom chambers).
* The heart is a double pump, with each side beating almost simultaneously.
* The heart is composed of cardiac muscle tissue, which produces the heartbeat when it contracts.
* The left ventricle pumps deoxygenated blood to the lungs, while the right ventricle pumps oxygenated blood to the lungs.

Systemic and Pulmonary Circulation
* The systemic circulation pumps oxygenated blood to all parts of the body and returns deoxygenated blood to the heart.
* The pulmonary circulation pumps blood from the heart to the lungs and back to the heart.
* The left ventricle has thicker muscle tissue than the right ventricle, which pumps deoxygenated blood to the lungs.

Changes in Blood Composition
* As blood moves around the animal, the basic compositions of blood cells and plasma remain the same, but the concentration of dissolved substances and gases changes depending on the organ it is passing through.
* As blood passes through all organs and tissues, the concentration of oxygen decreases and the concentration of carbon dioxide increases.
* As blood moves through all organs and tissues, nutrients such as glucose move out of the blood and into the cells, and wastes move in the opposite direction.
* In the liver, a decrease in digestive end products is evident once blood has passed through the liver.
* In the kidneys, the amount of urea is decreased because they filter nitrogenous wastes out of the blood.
* In the large intestine, water, salts, and vitamins are absorbed into the blood.
* When blood passes through endocrine glands, hormones are added to the blood.