Human Body | ICSE Class 7 Biology Notes

This note covers waste removal, the kidneys and urinary passages, sweat glands and lungs, urinary disorders, the brain, spinal cord and nerves, and the control and coordination of body activities.

What is excretion, and why does the body need it?

Definition: Excretion is the removal of wastes produced by the activities of cells, the basic living units of the body.

Cells carry out chemical reactions that keep the body alive. These reactions produce useful substances but also form wastes. Some wastes are harmful if they accumulate, so removing them is an essential part of keeping the body functioning.

Carbon dioxide is a waste gas formed when cells release energy from food. Urea is a nitrogen-containing waste, meaning that it contains the chemical element nitrogen. Urea is the major nitrogenous excretory product in humans.

How is excretion different from egestion?

Egestion is the removal of undigested and unabsorbed food material through the anus, the opening at the end of the digestive passage. This material has remained in the digestive passage; it is different from wastes produced by cellular activities.

Calling all material leaving the body “excretory waste” hides this distinction. The useful question is where the waste came from. Carbon dioxide produced by cells and undigested food removed from the gut have different origins and leave by different routes.

Blood, the fluid flowing through blood vessels, carries wastes to organs that remove them. Blood vessels are tubes carrying blood; an organ is a body part specialised for particular functions. Transport and removal are connected activities: wastes must reach the appropriate organ before they can leave the body.

Which organs remove excretory products?

The kidneys are the paired organs that filter blood and form urine, a fluid containing wastes dissolved in water. They are important excretory organs, but other organs also remove particular wastes. The lungs and sweat glands contribute to excretion in different ways.

What do the lungs and sweat glands remove?

The lungs, the breathing organs in the chest, remove carbon dioxide and water. Carbon dioxide reaches them in the blood and leaves during exhalation, which means breathing out. An organ used for breathing can therefore also serve an excretory function.

Sweat glands are structures in the skin that produce sweat, a watery fluid containing salts and small amounts of urea. The skin forms the body’s outer covering. These glands remove some waste substances when the fluid they produce reaches the skin surface.

Evaporation is the change of liquid water into water vapour, its gaseous form. Evaporation of sweat helps cool the body. Cooling is the primary function of sweat, although sweating also helps remove some wastes. These two functions should be distinguished.

How can their positions be represented?

Draw a simple human outline. Mark the lungs in the chest and the kidneys near the back of the abdomen. Label the outer covering as skin, and use a separate enlarged skin sketch to locate a sweat gland within it.

Attach the product to the correct organ when labelling. Carbon dioxide belongs with the lungs; urine belongs with the kidneys; sweat belongs with sweat glands. The three organs contribute to waste removal without producing the same fluid or removing identical substances.

Where are the parts of the urinary system, and what do they do?

The renal excretory system is the system that forms, carries, stores and releases urine. “Renal” means relating to the kidneys. It consists of two kidneys, two ureters, a urinary bladder and a urethra. It is also called the urinary system.

The kidneys are bean-shaped organs near the back wall of the abdomen. Each connects to a ureter, a tube carrying urine from a kidney to the urinary bladder. The two ureters provide separate routes from the two kidneys to a common storage organ.

The urinary bladder is a muscular sac that stores urine. It lies low in the trunk, below the kidneys. The urethra is the tube through which urine leaves the bladder and passes outside the body through the urinary opening.

How does urine move through these parts?

1. The kidneys form urine by removing wastes and water from the blood while useful substances are returned to the blood.
2. Urine moves from each kidney through its ureter towards the urinary bladder.
3. The bladder receives urine from the ureters and stores it before release.
4. Urine passes from the bladder through the urethra and leaves at the urinary opening.

Two bean-shaped kidneys appear above a rounded urinary bladder. A narrow ureter runs from each kidney to the bladder. The urethra continues below the bladder to the labelled urinary opening. Red and blue blood vessels lie between the kidneys.

See Fig. 7.6 in your NCERT textbook

Why do the names matter?

Ureter and urethra look similar as words but name different tubes. To distinguish them, identify their starting points and destinations. A ureter connects a kidney with the bladder; the urethra connects the bladder with the outside.

Similarly, forming urine and storing urine are different functions. A bladder label should be linked with storage, while a kidney label should be linked with filtering blood and forming urine. Tracing the complete route prevents these roles from being interchanged.

How do the kidneys filter blood and form urine?

Filtration means separating substances from a fluid by passing them across a filtering barrier. In the kidneys, this is part of the process by which wastes are removed from blood. Blood arriving at the kidneys contains both useful substances and substances that need removal.

A nephron is a tiny functional unit of a kidney that helps filter blood and form urine. The kidneys contain millions of nephrons. Their combined work makes the kidneys effective filtering organs without requiring the entire blood to become urine.

What is the basic sequence?

1. Blood carrying useful substances as well as wastes reaches the kidneys through blood vessels.
2. Filtration takes place in the kidneys through their numerous nephrons, separating fluid and dissolved substances from the blood.
3. Useful substances are absorbed back into the blood. This return is called reabsorption.
4. Wastes remaining dissolved in water form urine, which passes into the urinary passages for removal.

The word reabsorption is important because urine formation involves more than simply losing fluid from the blood. The body recovers useful substances. Water and salts are also regulated through the kidneys’ handling of the fluid that has been filtered.

The amount of water returned to the blood influences how much water is left in the urine. Thus, kidneys contribute both to removing wastes and to maintaining the body’s fluid balance. These functions occur together during the processing of blood.

What happens if wastes are not removed?

If the kidneys stop working, waste products start accumulating in the blood. This explains why kidney function is essential. Blood reaching a kidney brings substances for processing; urine leaving a kidney carries substances selected for removal from the body.

Note: Kidneys filter blood and form urine. Ureters carry urine, the bladder stores it, and the urethra allows it to leave. None of these urinary passages should be described as the organ that filters the blood.

What are urinary tract infections and kidney stones?

The urinary tract is the connected system through which urine is formed and passed out. It includes the kidneys and urinary passages. Two disorders affecting this system are urinary tract infection and kidney stones, which have different meanings.

What is a urinary tract infection?

A urinary tract infection is an infection in part of the urinary system. An infection occurs when disease-causing microorganisms enter and multiply in the body. Microorganisms are living things too small to see clearly without magnification. Bacteria commonly cause urinary tract infections.

The name is often shortened to UTI, meaning urinary tract infection. The term identifies the body system affected and the infectious nature of the disorder. It does not mean that a stone has formed, or that every part of the urinary tract is affected.

What is a kidney stone?

A kidney stone is a solid mass of crystallised salts formed within a kidney. Crystallised salts are salts arranged into solid crystals. Kidney stones are also called renal calculi; “renal” refers to the kidneys, and “calculi” means stones.

Both belong in a study of urinary disorders because they affect the urine-forming organs or their associated passages. They should be identified by their defining features: infection for a UTI, and a solid salt deposit for a kidney stone.

What are nerves, and how do they carry information?

The nervous system is the body’s system for receiving information, processing it and directing responses. Its main parts are the brain, spinal cord and nerves. Coordination means different organs working together so that their activities complement one another.

The brain is the main information-processing and coordinating organ in the head. The spinal cord is the long part of the nervous system running within the backbone, the bony column along the back. Nerves connect these centres with the rest of the body.

How is a nerve different from a neuron?

A tissue is a group of cells performing a specialised function. A neuron is a nerve cell specialised to receive and transmit information. A nerve is a bundle of nerve fibres; these fibres are long extensions of nerve cells. A nerve is therefore not simply another name for one neuron.

A nerve impulse is an electrical signal travelling along a nerve cell. Impulses allow information to pass between different parts of the body. Some carry information towards the brain or spinal cord, while others carry instructions towards body organs.

A stimulus is a change that can be detected and can produce a response. A response is the resulting action. Receptors are specialised structures that detect changes; they are usually located in sense organs such as the eyes, ears, nose and tongue.

How can a deliberate response be traced?

1. A receptor detects a change and starts information travelling as nerve impulses.
2. Nerves carry this information towards the brain, directly or through the spinal cord.
3. The brain processes the information and sends instructions through nerves to the muscles involved.
4. The muscles contract, or shorten, in response to these instructions and produce movement.

This sequence separates receiving information from carrying out an action. Nerves transmit the messages; muscles produce the movement. Writing, talking and moving a chair all require communication between coordinating centres and the muscles that perform the action.

Where is the cerebrum, and what does it do?

The brain lies within the skull, the bony case of the head. The skull protects this delicate organ, and fluid around the brain helps absorb shocks. Different parts of the brain carry out different functions while contributing to its overall coordinating role.

The cerebrum forms the major part of the human brain. It occupies the large upper region and belongs to the forebrain, the front major region of the brain. Its surface has prominent folds, and it is divided into left and right halves.

How does the cerebrum use information?

Different regions of the cerebrum receive and process information from the senses. This is called sensory information. Other regions help connect incoming information with information already stored. This supports complex activities such as thinking, memory and communication, rather than merely passing a message onwards unchanged.

Memory is the retention of information that can be used later. When incoming information is considered alongside stored information, the brain can decide how to respond. The cerebrum contains areas concerned with both receiving sensory information and controlling movement.

What are voluntary actions?

Voluntary actions are actions performed under conscious control, such as writing, talking or moving a chair. In these actions, the brain decides what movement to make and sends messages to the relevant muscles through the nervous system.

The cerebrum’s role in deciding and directing an action does not mean it performs the physical movement itself. Muscles carry out movement after receiving messages. Other brain regions also contribute, including those that make the movement precise and maintain balance.

When identifying the cerebrum on a drawing, look for the large folded region above the smaller structures at the back and base. Connect that location with its roles in processing sensory information, memory and the control of voluntary movement.

How do the cerebellum and medulla oblongata differ?

The cerebellum is a smaller region towards the back of the brain, below the cerebrum. It helps make voluntary movements precise and maintains posture, the position in which the body is held, and balance, the ability to remain steady.

The medulla oblongata, also called the medulla, lies at the lower part of the brain and connects with the spinal cord. It contains centres controlling several involuntary functions. Involuntary actions occur without being deliberately directed by conscious thought.

Which activities show their different functions?

Walking in a straight line, riding a bicycle and picking up a pencil require precise coordination. The cerebellum contributes to that precision. Deciding to pick up a pencil and coordinating the movement accurately are connected but distinguishable functions.

The medulla is associated with control of breathing and functions such as salivation and vomiting. Salivation means the production and release of saliva, the fluid in the mouth. Vomiting means expelling stomach contents through the mouth.

The side-sectional drawing shows a large folded cerebrum within the cranium, or skull. A smaller cerebellum lies towards the lower back. The medulla is labelled near the base, above the spinal cord. Use these positions to distinguish the three named regions.

See Fig. 6.3 in your NCERT textbook

How do the main nervous structures compare?

A reflex response is a rapid, automatic response to a stimulus. Spinal reflex responses are coordinated through the spinal cord. This is another example of different nervous structures contributing different functions to the control of the body.

Where is the spinal cord, and why is it important?

The spinal cord extends from the lower brain and runs within the vertebral column, another name for the backbone. The backbone protects the spinal cord. The cord is nervous tissue, whereas the backbone is the surrounding bony structure.

The brain and spinal cord together form the central nervous system, the main centres for processing information and controlling responses. Nerves connect these centres with the rest of the body, allowing information and instructions to travel between them.

How does the spinal cord link the body and brain?

Information from body parts can travel through nerves into the spinal cord and onwards to the brain. Messages from the brain can travel through the spinal cord and then through nerves to body parts. The cord is therefore an important communication route.

The spinal cord also coordinates spinal reflex responses. Pulling a hand away after touching a hot object illustrates a rapid response that does not wait for a deliberate decision. Information about the stimulus also travels to the brain.

This does not make the spinal cord a substitute for the brain. Deliberate thinking and the interpretation of complex information involve the brain. The nervous system combines rapid responses with communication to the brain, rather than using a single route for every action.

How can the nervous system be drawn?

In a human outline, draw the brain within the head and the spinal cord continuing down inside the backbone. Add branching nerves extending towards the trunk and limbs. Label brain, spinal cord and nerves, keeping the spinal cord distinct from its bony protection.

A complete explanation of the spinal cord should give both its location and its function. “Inside the backbone” identifies where it is protected; carrying messages and coordinating spinal reflex responses explain why it is needed.

How do the body’s systems work together?

The excretory and nervous systems have different main tasks. Excretion removes wastes, while nervous coordination organises responses and activities. Both support the functioning of the body’s cells, and neither is best understood as an isolated set of organs.

How is blood transport linked with excretion?

Blood carries wastes from cells to organs that remove them. Carbon dioxide reaches the lungs for release, while dissolved wastes reach the kidneys for processing. The kidneys return useful substances to the blood and send wastes out in urine.

This connection explains why the kidneys must receive blood to do their work. The urine pathway begins after urine has formed. Urine travels through the ureters, bladder and urethra; those tubes and storage spaces are different from the blood vessels supplying the kidneys.

How are messages linked with actions?

The nervous system receives information and sends instructions, but the responding organ carries out the action. Muscles shorten to produce movement. Brain regions contribute to planning, precision or involuntary control according to the activity involved.

The release of urine also involves nervous control. As the bladder fills, information about its stretching reaches the central nervous system. Nervous messages help bring about the muscular changes that allow stored urine to leave. Formation, storage and release remain distinct stages.

What should a complete explanation connect?

For an organ, connect location, structure and function. The kidneys are paired organs near the back of the abdomen that filter blood. The spinal cord is protected within the backbone and carries messages. These connections make the names meaningful.

For a process, trace the sequence from its starting point to its result. Follow wastes from cells to removal, urine from kidney to outside, or information from detection to response. Each sequence links several parts while preserving the particular job of each.

Glossary

• Excretion — The removal from the body of wastes produced by the activities of living cells.
• Egestion — The removal of undigested and unabsorbed food material from the digestive passage through the anus.
• Urea — A nitrogen-containing waste substance that is the major nitrogenous excretory product in humans.
• Nephron — A tiny functional unit in a kidney that helps filter blood and form urine.
• Ureter — A tube carrying urine from one kidney to the urinary bladder for storage.
• Urinary bladder — A muscular sac that receives urine from the ureters and stores it before release.
• Urethra — The tube carrying urine from the urinary bladder to the outside of the body.
• Urinary tract infection — An infection in part of the urinary system, commonly caused by bacteria.
• Kidney stone — A solid mass of crystallised salts formed within a kidney, also called a renal calculus.
• Neuron — A specialised nerve cell that receives information and transmits it through nerve impulses.
• Nerve — A bundle of nerve fibres carrying messages between coordinating centres and parts of the body.
• Cerebrum — The major part of the brain, supporting sensory processing, memory and control of voluntary movements.
• Cerebellum — A brain region concerned with precise voluntary movement and maintenance of posture and balance.
• Medulla oblongata — The lower brain region connected with the spinal cord and controlling several involuntary functions.
• Spinal cord — Nervous tissue within the backbone that carries messages and coordinates spinal reflex responses.

Common errors and misconceptions

• Misconception: Excretion and egestion mean the same thing. Correct: Excretion removes wastes produced by cellular activities, whereas egestion removes undigested and unabsorbed food material through the anus.
• Misconception: Kidneys remove every substance that reaches them in blood. Correct: Useful substances are absorbed back into the blood, while wastes dissolved in water leave as urine.
• Misconception: The urinary bladder makes urine. Correct: Kidneys form urine; ureters carry it to the urinary bladder, which stores it before release.
• Misconception: Ureters and the urethra are interchangeable names. Correct: Ureters connect kidneys to the bladder; the urethra carries urine from the bladder to the outside.
• Misconception: A urinary tract infection is a kidney stone. Correct: An infection involves disease-causing microorganisms, whereas a kidney stone is a solid mass of crystallised salts.
• Misconception: Cerebrum and cerebellum have identical functions. Correct: The cerebrum supports thinking and voluntary control; the cerebellum maintains posture, balance and precision of voluntary movement.
• Misconception: The spinal cord is the backbone. Correct: The spinal cord is nervous tissue running inside the backbone, the bony structure that protects it.

Exam-style questions with model answers

Q1. Define excretion and explain why the body needs it. [2 marks]

1. Excretion is the removal of wastes produced by the activities of living cells from the body.
2. It prevents harmful wastes from accumulating, helping the body’s cells and organs continue functioning.

Q2. Distinguish between a ureter and the urethra by stating the route each provides for urine. [2 marks]

1. A ureter carries urine from one kidney to the urinary bladder; there is one ureter from each kidney.
2. The urethra carries stored urine from the urinary bladder to the outside through the urinary opening.

Q3. Describe how the kidneys process blood to form urine. Give three points covering filtration, recovery of useful substances and removal of wastes. [3 marks]

1. Blood reaching the kidneys contains both useful substances and wastes. Numerous tiny functional units called nephrons help filter this blood.
2. Useful substances are absorbed back into the blood, so filtration does not mean that everything arriving at the kidneys is lost.
3. Wastes remaining dissolved in water form urine. This urine leaves the kidneys through the ureters on its way towards storage and removal.

Q4. Name three organs or structures that contribute to excretion and state what each removes: the kidneys, lungs and sweat glands. [3 marks]

1. The kidneys remove urea and other wastes with water and salts in urine. They filter blood and recover useful substances.
2. The lungs remove carbon dioxide and water. Carbon dioxide transported from the body’s cells leaves the lungs during breathing out.
3. Sweat glands in the skin remove water, salts and small amounts of urea in sweat. Sweat evaporation also helps cool the body.

Q5. Compare the cerebrum, cerebellum and medulla oblongata. Give the location and a main function of each in three separate points. [3 marks]

1. The cerebrum forms the large upper part of the brain. It supports sensory processing, memory and the control of voluntary movements.
2. The cerebellum lies below the cerebrum towards the back. It maintains posture and balance and contributes to precise voluntary movement.
3. The medulla oblongata lies in the lower brain, connected with the spinal cord. It controls several involuntary functions, including breathing.

Q6. Describe the human urinary system in five points: kidney position and function; ureters; bladder; urethra; and the complete route of urine. [5 marks]

1. The two bean-shaped kidneys lie near the back wall of the abdomen. They filter blood and form urine containing wastes dissolved in water.
2. Each kidney connects to a ureter, a tube that carries urine down towards the urinary bladder.
3. The urinary bladder is a muscular sac below the kidneys. It receives urine from the ureters and stores it before release.
4. The urethra carries urine from the bladder to the outside of the body, ending at the urinary opening.
5. The complete route is kidney, ureter, urinary bladder, urethra and urinary opening. Formation takes place in the kidneys, while storage takes place in the bladder.

Q7. Explain the nervous system in five points covering its purpose, brain, spinal cord, nerves and muscle response. Include the location of the brain and spinal cord. [5 marks]

1. The nervous system receives information, processes it and directs responses. Its coordinating role allows different body parts to work together.
2. The brain lies inside the skull and acts as the main coordinating centre. Its different regions contribute to different functions.
3. The spinal cord runs within the backbone. It carries messages between the brain and body and coordinates spinal reflex responses.
4. Nerves connect the brain and spinal cord with other body parts. They carry information towards these centres and instructions towards organs.
5. Muscles carry out movement after receiving nervous messages. Their contraction produces the physical response, while nerves provide the communication needed to direct it.

Q8. Distinguish a urinary tract infection from a kidney stone by defining each. [2 marks]

1. A urinary tract infection is an infection in part of the urinary system, commonly caused by bacteria.
2. A kidney stone is a solid mass of crystallised salts formed within a kidney.

Key takeaways

• Excretion removes wastes produced by cells, while egestion removes undigested and unabsorbed food material through the anus.
• Kidneys filter blood, recover useful substances and form urine containing wastes dissolved in water.
• Urine travels from each kidney through a ureter to the bladder, then leaves through the urethra.
• Lungs remove carbon dioxide and water; sweat glands remove water, salts and small amounts of urea.
• Urinary tract infections involve infection, while kidney stones are solid masses of crystallised salts.
• The cerebrum supports sensory processing and voluntary control; the cerebellum maintains balance and precision of movement.
• The medulla oblongata connects with the spinal cord and controls several involuntary functions, including breathing.
• The spinal cord carries messages and coordinates spinal reflex responses; nerves connect coordinating centres with other body parts.

Test yourself

Why is removing undigested food described as egestion?

It removes material remaining in the digestive passage, rather than wastes produced by cellular activities.

What is a nephron?

A nephron is a tiny functional unit of a kidney that helps filter blood and form urine.

Which structure stores urine, and which tube carries it outside?

The urinary bladder stores urine; the urethra carries it from the bladder to the outside.

How does sweating contribute to both excretion and cooling?

Sweat removes water, salts and small amounts of urea. Its evaporation helps cool the body surface.

What do the letters UTI stand for?

They stand for urinary tract infection, meaning an infection in part of the urinary system.

Which part of the brain helps maintain posture and balance?

The cerebellum maintains posture and balance and contributes to the precision of voluntary movements.

How does the spinal cord differ from the backbone?

The spinal cord is nervous tissue; the backbone is the bony structure around it that provides protection.

Why does a muscle need a nervous message for a directed movement?

The message communicates the instruction for action. The muscle then contracts to produce the movement.