Life Processes: Nutrition and Respiration

Life Processes

Life processes refer to the essential activities and functions that living organisms perform to sustain their lives and maintain their existence. These processes are fundamental for the survival and functioning of all living organisms, from the simplest single-celled organisms to complex multicellular organisms like humans. Life processes ensure that organisms can obtain energy, grow, respond to their environment, and reproduce.

Some of the major life processes include:

1. Nutrition: Nutrition is the process by which organisms obtain and utilise nutrients (organic and inorganic substances) from their environment as a source of energy and raw materials for growth, repair, and maintenance.
2. Respiration: Respiration is the process by which organisms release energy from the nutrients they have obtained through nutrition. During respiration, organic molecules (such as glucose) are broken down in the presence of oxygen, releasing energy in the form of adenosine triphosphate (ATP) that cells can use for various metabolic activities. Some organisms, like anaerobic bacteria, can respire without oxygen, but most require oxygen for this process.
3. Transportation (Circulation): In multicellular organisms, especially those with complex body structures, the transportation of essential substances like nutrients, oxygen, and waste products is vital. Specialised systems, such as the circulatory system in animals or vascular tissues in plants, facilitate the movement of these substances between cells and different parts of the organism.
4. Excretion: Excretion is the removal of waste products and harmful substances, such as carbon dioxide, urea, and excess salts, from the organism's body. These waste materials are produced during metabolic processes and need to be eliminated to maintain a healthy internal environment.



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5. Response to Stimuli: Organisms can respond to changes in their environment through various mechanisms. This includes detecting and reacting to external stimuli such as light, temperature, touch, and chemicals. Responses can be immediate, like a reflex action, or more complex, involving the nervous and endocrine systems in animals.
6. Growth: Growth is the process by which an organism increases in size, often through cell division and the accumulation of new cells. It is an essential life process that allows organisms to develop, repair damaged tissues, and reach maturity.
7. Reproduction: Reproduction is the process by which organisms produce offspring, ensuring the continuation of their species. Reproduction can be asexual, where a single parent produces genetically identical offspring, or sexual, where two parents contribute genetic material to produce genetically diverse offspring.



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Nutrition

Nutrition is one of the fundamental life processes that organisms engage in to obtain the energy and materials necessary for their growth, maintenance, and survival. It involves the acquisition and utilisation of food or nutrients from the external environment.

The primary source of energy and materials for living organisms is food. Food provides the necessary nutrients required for various metabolic activities. There are different modes through which organisms obtain nutrition.

Modes of Nutrition

1. Autotrophic Nutrition: Autotrophic organisms, such as green plants and some bacteria, can synthesise their own food using simple inorganic substances like carbon dioxide and water. They utilise sunlight and chlorophyll in a process known as photosynthesis to convert these raw materials into carbohydrates, which serve as an energy source for the plant. Excess carbohydrates are stored as starch for future use.
2. Heterotrophic Nutrition: Heterotrophic organisms, including animals and fungi, cannot produce their own food. Instead, they rely on consuming complex organic substances from other sources. These complex substances need to be broken down into simpler forms before they can be used by the organism. Enzymes play a crucial role in breaking down these complex molecules into usable components. The survival of heterotrophic organisms depends either directly or indirectly on autotrophs. This interdependence highlights the importance of the food chain, where energy and nutrients flow from autotrophs to heterotrophs.

Types of Nutrients

1. Macronutrients: These are nutrients required in large quantities and include carbohydrates, proteins, and fats. They serve as sources of energy and are essential for various physiological functions.
   Both autotrophic and heterotrophic organisms have mechanisms to store excess energy. In plants, surplus carbohydrates are stored as starch, while animals store energy in the form of glycogen.
2. Micronutrients: These are nutrients required in smaller quantities but are vital for specific biochemical processes. Micronutrients include vitamins and minerals, which play crucial roles in maintaining health.

Digestion and Absorption (In Animals)

After consuming food, animals go through the process of digestion. This process involves breaking down complex food molecules into simpler forms through mechanical and enzymatic processes.
The absorbed nutrients are transported through the bloodstream to cells throughout the organism's body, where they are used for energy production, growth, and repair.

Metabolism

Once nutrients are absorbed into cells, they undergo metabolic processes. These processes involve converting nutrients into energy (through cellular respiration) and using them to build and repair tissues and support various biochemical reactions.
Metabolism also includes the storage of excess nutrients for future use.

Autotrophic Nutrition

Autotrophic nutrition is a mode of nutrition in which organisms are capable of producing their own food from simple inorganic substances like carbon dioxide (CO₂) and water (H₂O), using an external energy source. This process is primarily carried out by autotrophic organisms, such as green plants, some bacteria, and algae. Autotrophic nutrition is exemplified by photosynthesis.
It is the key process in autotrophic nutrition which occurs in specialised organelles called chloroplasts in plant cells.

1. Energy Source: The primary source of energy for autotrophic organisms is sunlight. Sunlight provides the energy required for the synthesis of food, which is a vital process for the growth and sustenance of autotrophic organisms.
2. Carbon Dioxide Uptake: Autotrophic organisms obtain carbon dioxide (CO₂) from the surrounding atmosphere. Carbon dioxide is taken up through tiny pores called stomata, which are mainly found on the surfaces of leaves. These stomata allow the exchange of gases, including the uptake of carbon dioxide required for photosynthesis.
3. Water and Nutrient Uptake: In addition to carbon dioxide, autotrophic organisms require water (H₂O) and various inorganic nutrients for photosynthesis. Water is absorbed by the roots of plants from the soil, and it is transported to the leaves. The roots also take up essential nutrients like nitrogen, phosphorus, iron, and magnesium from the soil. These nutrients are crucial for the synthesis of various organic molecules.

Photosynthesis Process

Photosynthesis is the essential process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose (a type of sugar) and oxygen.

The process of photosynthesis involves several stages:

1. Absorption of Light Energy: The process begins with the absorption of sunlight by special pigments called chlorophyll, which are found in chloroplasts within plant cells. Chlorophyll is like a solar panel for plants.
2. Conversion of Light Energy: The absorbed sunlight energy is converted into chemical energy in the form of high-energy molecules like ATP and NADPH. This conversion occurs in the thylakoid membranes of chloroplasts during the light-dependent reactions.
3. Splitting of Water Molecules: In the light-dependent reactions, water molecules (H₂O) are split into oxygen (O₂), protons (H⁺ ions), and electrons (e^-). This splitting of water is a source of oxygen production, which is released into the air as a byproduct.
4. Reduction of Carbon Dioxide: Carbon dioxide (CO₂) from the atmosphere is taken in through tiny openings called stomata on the leaves. It is then reduced and converted into carbohydrates, primarily glucose, in the presence of sunlight and chlorophyll. This step occurs in the Calvin cycle, which is the light-independent phase of photosynthesis.
5. Formation of Sugars: The carbohydrates, such as glucose and sucrose, are the primary end products of photosynthesis. These sugars serve as an energy source for the plant's metabolic processes and are also used for growth and reproduction.
6. Oxygen Release: A significant by-product of photosynthesis is the release of oxygen (O₂) into the atmosphere. This oxygen is essential for the respiration of various organisms, including humans, and plays a crucial role in maintaining the balance of atmospheric gases.

Overall Equation for Photosynthesis:

The overall chemical equation for photosynthesis can be summarised as follows:

Heterotrophic Nutrition

Heterotrophic nutrition is a mode of nutrition in which organisms obtain their energy and essential nutrients by consuming other organisms or organic matter derived from them. This mode of nutrition is in contrast to autotrophic nutrition, where organisms can produce their own organic molecules from inorganic substances like carbon dioxide and water, typically using sunlight as an energy source. Heterotrophic organisms lack the ability to synthesise their own food and rely on external sources for nutrition.

Dependence on Other Organisms: Heterotrophic organisms, also known as heterotrophs, cannot perform photosynthesis or other similar processes to produce organic compounds from simple inorganic substances. Instead, they depend on ready-made organic molecules, such as carbohydrates, proteins, and lipids, to fulfil their energy and nutritional needs.

Types of Heterotrophic Nutrition

1. Holozoic Nutrition: In holozoic nutrition, organisms ingest complex food particles, such as plants or other animals, through various means like swallowing, biting, or engulfing. The ingested food undergoes a series of digestive processes, including mechanical and chemical digestion, within specialised digestive organs or systems. These processes break down complex molecules into simpler forms that can be absorbed and utilised by the organism. Holozoic nutrition is commonly found in animals, including humans.
2. Saprophytic Nutrition: Saprophytic nutrition is characteristic of organisms known as saprophytes or decomposers. These organisms feed on dead and decaying organic matter, such as fallen leaves, wood, or dead animals. They secrete digestive enzymes onto the organic material, breaking it down externally into simpler substances. Once the organic matter is partially decomposed, the saprophytic organism absorbs the resulting nutrients. Fungi, certain bacteria, and some insects follow saprophytic nutrition.
3. Parasitic Nutrition: Parasitic nutrition involves organisms known as parasites that live in or on other living organisms, known as hosts. Parasites derive their nutrients and energy from the host organism, often at the expense of the host's health or well-being. Parasites have evolved various adaptations to attach to or penetrate their hosts and access the necessary nutrients. Examples of parasitic organisms include ticks, lice, tapeworms, and certain plants like Cuscuta.
4. Digestion, Absorption, and Assimilation: In heterotrophic nutrition, the process of digestion is essential to break down complex organic molecules into simpler forms that can be absorbed by the organism. Absorption occurs primarily in the digestive system or specialised structures designed for nutrient uptake. Once absorbed, the nutrients are transported throughout the organism's body, where they are assimilated or used for growth, energy production, and tissue repair.

Nutrition in Amoeba

Amoeba is a unicellular, microscopic organism belonging to a group of protists. It follows the holozoic mode of nutrition, which means it engulfs and digests solid food particles. Here's a step-by-step explanation of how nutrition occurs in amoeba:

1. Ingestion: Amoeba captures its food through a process called phagocytosis. When it encounters a suitable food particle, such as a small algae or bacteria, it extends its cell membrane to surround and engulf the food particle, forming a temporary structure known as a food vacuole.
2. Digestion: Once the food particle is enclosed within the food vacuole, amoeba secretes digestive enzymes into the vacuole. These enzymes start breaking down the complex organic molecules of the food into simpler forms. This process is similar to the digestion that occurs in the stomach of higher animals.
3. Absorption: As digestion continues inside the food vacuole, the nutrients released from the digested food pass through the vacuole's membrane and into the cytoplasm of the amoeba. This is the absorption phase, where simple molecules such as amino acids, sugars, and other nutrients are taken up by the amoeba's cell for energy and growth.
4. Assimilation: After absorption, the simple nutrients are utilised by the amoeba for various metabolic processes, including energy production, growth, and repair of cellular structures. This phase is known as assimilation, where the amoeba incorporates the absorbed nutrients into its own cellular activities.
5. Egestion: Any undigested or indigestible remnants of the food particle, along with waste materials, are expelled from the amoeba's cell. This process is called egestion and ensures that the amoeba gets rid of unnecessary or harmful substances.

Amoeba's ability to adapt its cell membrane to surround and engulf food particles allows it to feed on a variety of microorganisms and organic matter present in its aquatic environment. This holozoic mode of nutrition enables amoeba to meet its energy and nutritional requirements as a unicellular organism.

Nutrition in Human Beings

Nutrition in human beings involves a series of processes that occur in the digestive system, which is essentially a long tube known as the alimentary canal. Here is an explanation of the various stages of nutrition in human beings:

Ingestion (Mouth)

1. Nutrition begins with the process of ingestion, where food is taken into the mouth. In the mouth, mechanical digestion starts as teeth break down the food into smaller pieces.
2. The tongue helps in moving food around while chewing, and salivary glands secrete saliva, which contains an enzyme called salivary amylase that starts breaking down complex carbohydrates (starch) into simpler sugars.

Digestion (Stomach)

1. After chewing, the food is swallowed and travels down the oesophagus to reach the stomach.
2. In the stomach, the food mixes with gastric juices that contain hydrochloric acid and the enzyme pepsin.
3. Hydrochloric acid creates an acidic environment, aiding in the digestion of proteins by pepsin.
4. The result is partially digested food known as chyme.

Small Intestine

1. Chyme is then released into the small intestine, where most of the digestion and absorption of nutrients occurs.
2. The pancreas secretes pancreatic juice into the small intestine, which contains enzymes like trypsin (for protein digestion) and lipase (for fat digestion).
3. The liver produces bile, stored in the gallbladder, which is released into the small intestine to emulsify fats, increasing their surface area for digestion.
4. The walls of the small intestine contain numerous finger-like projections called villi and microvilli that increase the surface area for absorption.
5. Nutrients, including glucose, amino acids, and fatty acids, are absorbed into the bloodstream through the walls of the small intestine.

Absorption and Assimilation

1. Absorbed nutrients are transported through the bloodstream to cells and tissues throughout the body.
2. Glucose provides energy for cellular processes.
3. Amino acids are used for building and repairing tissues.
4. Fatty acids and glycerol are used for energy and structural components of cell membranes.
5. Vitamins and minerals are essential for various metabolic functions.

Large Intestine

1. The remaining undigested and unabsorbed material enters the large intestine, where the absorption of water and minerals takes place.
2. This results in the formation of faeces.

Rectum and Anus

1. Faeces are stored in the rectum until they are eliminated from the body through the anus during the process of defecation.

Respiration

1. Respiration is a fundamental biological process that occurs within the cells of all living organisms, including humans. It serves as the primary mechanism for extracting energy from the food we consume. Think of it as the power plant of your body, converting food into the energy needed for various activities, such as moving, thinking, and even growing.
2. Respiration is vital because it provides the energy necessary for all life processes. Without this energy, our bodies would be unable to function efficiently.

Respiration in Plants

Respiration in plants is a vital process through which they obtain energy, similar to how animals do. Plants, like animals, require oxygen for respiration and release carbon dioxide as a byproduct. This exchange of gases, oxygen and carbon dioxide, is central to plant respiration.

Plants have a branching structure, which results in a large surface area relative to their volume. This structural feature allows them to obtain oxygen through diffusion, effectively supplying all plant cells with the required oxygen for respiration. This diffusion process takes place in various parts of the plant, including the roots, stems, and leaves.

1. Respiration in Roots: Roots of a plant absorb oxygen from the air present in the soil by utilising tiny structures called root hairs. These root hairs come into contact with the air in the soil, enabling the diffusion of oxygen from the soil particles into the root cells. Additionally, carbon dioxide produced during root cell respiration diffuses out through the same root hairs.
2. Respiration in Stems: The stems of herbaceous plants (soft, non-woody stems) contain stomata, small openings that facilitate the exchange of respiratory gases. Oxygen from the surrounding air diffuses into herbaceous stems through stomata, providing oxygen to all stem cells for respiration. In contrast, woody stems, found in large plants and trees, have lenticels in their bark, which serve as openings for gas exchange. Oxygen diffuses into woody stems through lenticels, reaching the inner stem cells for respiration, while carbon dioxide produced during respiration exits through the same lenticels.
3. Respiration in Leaves: Leaves possess tiny pores known as stomata, through which the exchange of respiratory gases occurs via diffusion. During the day, when photosynthesis takes place, leaves produce oxygen, some of which is used for leaf cell respiration, while the rest diffuses into the air through stomata. Simultaneously, carbon dioxide generated through respiration is consumed by photosynthesis, and additional carbon dioxide is taken in from the air. At night, when photosynthesis ceases, oxygen from the air diffuses into leaves for respiration, and carbon dioxide produced during respiration exits through stomata.

Respiration in Animals

Respiration in animals is the biological process through which animals extract energy from organic molecules, typically glucose, and release carbon dioxide as a waste product. This energy is essential for various life processes, including movement, growth, and maintaining bodily functions. Animal respiration can vary in complexity and involves different organs and mechanisms depending on the type of animal.

Purpose of Respiration

The primary purpose of respiration in animals is to generate energy in the form of adenosine triphosphate (ATP). This energy is crucial for powering cellular activities, such as muscle contractions, digestion, and maintaining body temperature.

Respiratory Organs

Animals have specialised respiratory organs that facilitate the exchange of gases, primarily oxygen and carbon dioxide, with their surroundings. The type of respiratory organ varies among different animal species.

Types of Respiration in Animals

There are several modes of respiration in animals, including:

1. Cutaneous Respiration: Some animals, like earthworms, rely on their skin to absorb oxygen directly from the environment. Their skin is thin and moist, which facilitates gas exchange.
2. Gill Respiration: Aquatic animals, such as fish, prawns, and mussels, use gills as their respiratory organs. Gills extract dissolved oxygen from water and release carbon dioxide.
3. Tracheal Respiration: Insects like grasshoppers, cockroaches, and mosquitoes have a network of tiny tubes called tracheae that deliver air directly to cells for gas exchange. These tubes connect to small openings called spiracles on the insect's body.
4. Pulmonary Respiration: Land animals, including mammals like humans, birds, and reptiles, typically have lungs as their primary respiratory organs. These animals breathe in air through the nose or mouth, and the lungs facilitate the exchange of oxygen and carbon dioxide with the bloodstream.

Gaseous Exchange

Regardless of the respiratory organ, all animals share common features in their respiratory systems. These include:

1. Large Surface Area: Respiratory organs have a large surface area to maximise contact with oxygen from the environment.
2. Thin Walls: Thin walls of respiratory organs enable efficient diffusion and exchange of respiratory gases (oxygen and carbon dioxide) between the organism and its surroundings.
3. Rich Blood Supply: Respiratory organs are well-vascularised, ensuring that oxygen can be transported via the bloodstream to various tissues. Carbon dioxide is also picked up by the blood and transported back to the respiratory organ for elimination.

Rate of Respiration

The rate of respiration varies among animals and can be influenced by factors such as activity level, environmental conditions, and metabolic needs. For example, animals engaged in physical activity or in low-oxygen environments may respire more rapidly to meet their energy demands.

Differences Between Respiration in Plants and Animals

1. Individual Respiration: Unlike animals, where respiration occurs as a unified process within a single organism, different parts of a plant, such as the roots, stem, and leaves, perform respiration individually.
2. Limited Gas Transport: In plant respiration, there is minimal transport of respiratory gases between different parts of the plant. In contrast, animals have elaborate circulatory systems that transport gases over long distances during respiration.
3. Rate of Respiration: Plant respiration generally occurs at a slower rate compared to respiration in animals, which typically happens at a much faster pace.

Respiration in Humans

Respiration in humans, often referred to as the human respiratory system, is the complex biological process that allows our bodies to exchange gases with the environment, primarily involving the intake of oxygen (O₂) and the removal of carbon dioxide (CO₂). This process is essential for generating energy and maintaining the body's metabolic functions. Let's delve into the details of respiration in humans:

Key Components of Human Respiration:

Respiratory Organs

1. Lungs: Lungs are the central organs of the human respiratory system. They are responsible for the exchange of gases. Each lung is divided into lobes, with the right lung having three and the left lung having two lobes.
2. Nasal Cavity and Mouth: Air enters the respiratory system through the nasal cavity or mouth. The nasal passages filter, humidify, and warm the incoming air, while the mouth serves as an alternative passage for air intake.
3. Trachea (Windpipe): After entering through the nose or mouth, air passes into the trachea, a tube composed of cartilage rings that prevent it from collapsing. The trachea then branches into the bronchi, which further divides into bronchioles, leading to the lungs.

Gas Exchange

1. Alveoli: Within the lungs, air reaches tiny sacs called alveoli, which have thin walls rich in blood vessels. It is in the alveoli that the actual exchange of gases occurs. Oxygen from inhaled air diffuses into the bloodstream, while carbon dioxide from the blood diffuses into the alveoli to be exhaled.
2. Diaphragm and Intercostal Muscles: Breathing is facilitated by the diaphragm, a dome-shaped muscle located below the lungs, and the intercostal muscles, which are situated between the ribs. When these muscles contract, the thoracic cavity expands, causing inhalation. Relaxation of these muscles leads to exhalation.

Process of Respiration

Respiration operates as a complex set of chemical reactions within your cells.

1. Inhalation (Breathing In)

When we inhale, the diaphragm contracts and moves downward, while the intercostal muscles expand the ribcage. This expansion increases the volume of the thoracic cavity, causing a decrease in air pressure within the lungs. As a result, air rushes into the lungs, carrying oxygen with it.

2. Gas Exchange

As the inhaled oxygen enters the bloodstream in the alveoli, it binds to haemoglobin in red blood cells and is transported throughout the body.

3. Oxygen Transport

Oxygen molecules bind to a protein called haemoglobin in red blood cells, forming oxyhemoglobin.
The oxygen-rich blood then gets pumped by the heart to various parts of the body.

4. Food Digestion

Simultaneously the body breaks down food molecules, particularly carbohydrates, in your stomach and intestines to make glucose.

5. Cellular Respiration

Within cells, glucose (a sugar) is broken down in a series of chemical reactions. This process is called cellular respiration. The primary goal of cellular respiration is to produce a molecule called ATP (adenosine triphosphate), which stores and releases energy for various cellular functions. The breakdown can happen through two main pathways: glycolysis and subsequent cellular respiration, which may be aerobic or anaerobic, depending on the availability of oxygen.

1. Glycolysis: Glycolysis is the first stage of glucose breakdown, and it occurs in the cytoplasm of the cell, outside the mitochondria (the energy-producing organelles).
   During glycolysis, a molecule of glucose, which has six carbons, is split into two three-carbon molecules called pyruvate.
   Glycolysis consumes a small amount of energy (ATP) but ultimately produces more ATP and NADH, another energy-rich molecule.
2. Pyruvate Fate: What happens to the pyruvate molecules next depends on whether oxygen is present or not.
   If oxygen is available, the pyruvate molecules enter the mitochondria, where they undergo further breakdown via the process of aerobic respiration.
   In the absence of oxygen, pyruvate can follow an alternative pathway involving anaerobic respiration.

6. Types of Respiration

Aerobic Respiration

Aerobic respiration is the most common and efficient type of respiration in living organisms.

Key Points:

1. Oxygen Presence: Aerobic respiration occurs in the presence of an adequate supply of oxygen (O₂). Oxygen is essential for this process to take place.
2. Energy Production: During aerobic respiration, the breakdown of food molecules, such as glucose, is thorough and complete. It leads to the production of a large amount of energy in the form of ATP (adenosine triphosphate).
3. Location: Most of the aerobic respiration takes place in the mitochondria, which are small structures within the cells.
4. End Products: The end products of aerobic respiration are carbon dioxide (CO₂), water (H₂O), and a significant amount of ATP. Carbon dioxide and water are considered waste products and are eliminated from the body.
5. Efficiency: Aerobic respiration is highly efficient, yielding a substantial amount of energy per glucose molecule.



6. Examples: This type of respiration is the primary method used by humans, animals, and many microorganisms to obtain energy. It's the reason we breathe in oxygen, which is essential for aerobic respiration.

Anaerobic Respiration

Anaerobic respiration, on the other hand, is a type of respiration that occurs when there is a shortage of oxygen.

Key Points:

1. Oxygen Absence: Anaerobic respiration takes place in the absence or limited supply of oxygen. When cells can't access enough oxygen quickly, they resort to this type of respiration.
2. Energy Production: During anaerobic respiration, glucose or other organic molecules are only partially broken down. This leads to the production of a small amount of energy.
3. Location: Anaerobic respiration typically occurs in the cytoplasm of cells, not in the mitochondria.
4. End Products: The end products of anaerobic respiration can vary depending on the organism and circumstances. In humans and animals, it often results in the production of lactic acid or ethanol (ethyl alcohol), along with a limited amount of ATP.
5. Efficiency: Anaerobic respiration is less efficient than aerobic respiration in terms of energy production. It generates far less ATP per glucose molecule.



6. Examples: Anaerobic respiration is commonly observed in microorganisms like yeast when they ferment sugars to produce ethanol (used in baking and brewing) and in our muscles during intense physical activity, leading to the buildup of lactic acid (causing muscle soreness).

7. ATP Production

Throughout the breakdown of glucose, the cells generate ATP, which is the primary energy currency used for various cellular functions.
ATP stores energy in its chemical bonds and releases it when needed for activities like muscle contractions, cell division, and active transport.

8. Waste Products

The waste products of glucose breakdown depend on whether it follows an aerobic or anaerobic pathway. In aerobic respiration, the waste products are carbon dioxide (CO₂) and water (H₂O), while in anaerobic respiration, they can be lactic acid or ethanol, depending on the organism.

9. Breathing out (Exhalation)

Carbon dioxide is expelled from the body through exhalation, where it is released into the atmosphere.

10. Regulation of Respiration

The rate and depth of respiration are regulated by the respiratory centre located in the brainstem. It monitors factors such as blood oxygen levels (sensed by chemoreceptors), blood pH, and carbon dioxide levels. If these factors deviate from their set points, the respiratory centre adjusts the breathing rate and depth to maintain homeostasis.