Transportation of Materials — Class 7 Science

The circulatory system is responsible for transporting blood, nutrients, oxygen, and waste products throughout the body. It consists of the heart, blood vessels, and blood.

The circulatory system performs the following functions:

• Transports oxygen from lungs to all body parts
• Transports carbon dioxide from body parts to lungs for removal
• Carries digested food (nutrients) to all cells
• Carries waste materials to kidneys for excretion
• Transports hormones from glands to target organs

Important: The human circulatory system is a closed circulatory system, meaning blood flows through a closed network of blood vessels and never leaves the vessels.

The heart is a cone-shaped muscular organ, about the size of a fist. It is located between the lungs in the middle of the rib cage, tilting slightly towards the left side.

Structure of the Heart:

• The human heart has four chambers
• Upper chambers: Left atrium and Right atrium (plural: atria)
• Lower chambers: Left ventricle and Right ventricle
• Atria are thin-walled (they receive blood)
• Ventricles are thick-walled (they pump blood out)
• The left ventricle has the thickest walls because it pumps blood to the entire body
• A muscular wall called the septum separates the left and right sides of the heart

Flow of blood in the heart:

Blood flows from atria (upper chambers) to ventricles (lower chambers). The ventricles then pump blood into arteries to carry it to different parts of the body.

Double circulation: Blood passes through the heart twice in one complete cycle. First, deoxygenated blood goes from the heart to the lungs and back (pulmonary circulation). Then, oxygenated blood goes from the heart to the body and back (systemic circulation).

Blood vessels are tubes through which blood flows in our body. There are three types of blood vessels:

Key exception: The pulmonary artery carries deoxygenated blood (from heart to lungs), and the pulmonary vein carries oxygenated blood (from lungs to heart). These are the only exceptions.

Blood is a fluid connective tissue that serves as a medium of transport. It consists of blood cells suspended in a fluid called plasma.

1. Plasma:

• Pale yellow-coloured liquid
• Contains about 90% water
• Carries dissolved salts, proteins, glucose, urea, minerals, and hormones
• Transports digested food, waste products, and CO2

2. Red Blood Cells (RBCs / Erythrocytes):

• Most numerous blood cells
• Contain haemoglobin - a red-coloured pigment that gives blood its red colour
• Haemoglobin combines with oxygen to form oxyhaemoglobin
• Responsible for transporting oxygen from lungs to all body parts
• RBCs do not have a nucleus (in mammals)

3. White Blood Cells (WBCs / Leucocytes):

• Larger than RBCs but fewer in number
• Help the body fight diseases by destroying infectious agents (germs, bacteria)
• Act as soldiers of the body

4. Platelets (Thrombocytes):

• Play an important role in clotting of blood
• Block the injured area and prevent excessive blood loss from damaged blood vessels
• Without platelets, even a small cut could be life-threatening

The heart beats continuously to pump blood throughout the body.

Heartbeat:

• The rhythmic contraction and relaxation of the heart is called a heartbeat
• A normal resting heart beats about 70-80 times per minute in an adult
• The instrument used to listen to heartbeat is called a stethoscope

Pulse:

• Each time the ventricles contract, blood is pumped into the arteries
• This creates a wave-like expansion in the arteries called the pulse
• Since the pulse results from ventricular contraction, the pulse rate equals the heartbeat rate
• Pulse can be felt at the wrist (radial artery) or neck (carotid artery)
• Pulse rate increases during exercise, fever, or excitement

How to check pulse: Place your index and middle fingers on the inside of the wrist (below the thumb). Count the number of pulses felt in one minute.

Blood group is a classification of blood based on the presence or absence of certain substances (antigens) on the surface of red blood cells.

ABO Blood Group System:

There are four main blood groups: A, B, AB, and O.

Key terms:

• Universal Donor: Blood group O (can donate to all groups)
• Universal Recipient: Blood group AB (can receive from all groups)

Why is blood grouping important? Before a blood transfusion, the blood groups of the donor and recipient must be matched. Mismatched blood can cause clumping (agglutination) of blood cells, which can be fatal.

Plants also need to transport water, minerals, and food to different parts. This is done by the vascular system, which consists of two types of conducting tissues.

Together, xylem and phloem form vascular bundles that run throughout the plant like a network of pipes.

Note: The transport of food from leaves to other parts of the plant through phloem is called translocation.

Roots absorb water and dissolved minerals from the soil. This process involves osmosis.

Osmosis: The movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.

How roots absorb water:

• Root hair cells have thin walls and a large surface area
• The concentration of water inside the root cells is lower than in the soil
• Water moves from the soil into the root hair cells by osmosis
• From root hair cells, water moves cell by cell to the xylem
• Xylem then transports water upward to stems and leaves

Role of root hairs: Root hairs are tiny, hair-like extensions of root cells. They greatly increase the surface area of the root for better absorption of water and minerals.

Transpiration is the loss of water in the form of water vapour from the aerial parts (mainly leaves) of a plant through tiny pores called stomata.

How transpiration works:

• Stomata are tiny pores on the surface of leaves
• Water evaporates from the cells inside the leaf through stomata
• This creates a suction force (transpiration pull) that pulls water upward through the xylem
• This is the main force that helps water rise from roots to tall tree tops

Significance of Transpiration:

• Creates a suction pull that helps in the ascent of sap (upward movement of water)
• Helps in the absorption of water and minerals from the soil
• Cools the plant (similar to how sweating cools our body)
• Removes excess water from the plant
• Helps in regulating the temperature of the plant body

The process of removing waste products produced during life processes from the body is called excretion. The human urinary system (excretory system) removes nitrogenous wastes from the body in the form of urine.

Organs of the Excretory System:

• Kidneys: A pair of bean-shaped organs located on either side of the spine. They filter blood and remove nitrogenous wastes (urea), excess water, and salts. Each kidney contains millions of tiny filtering units called nephrons. Nephrons are surrounded by capillaries and filter waste from blood to form urine.
• Ureters: A pair of tubes that carry urine from the kidneys to the urinary bladder.
• Urinary Bladder: A muscular, balloon-like organ that stores urine until it is expelled from the body.
• Urethra: The tube through which urine is passed out of the body.

Path of urine: Kidneys (filter blood) → Ureters → Urinary Bladder (storage) → Urethra (expulsion)

Dialysis is an artificial process that performs the function of kidneys when they fail to work properly due to disease or damage.

How dialysis works:

• Blood from the patient is passed through a machine containing a dialyser
• The dialyser has a semipermeable membrane (artificial kidney)
• Waste products like urea and excess salts pass through the membrane into a special fluid called dialysing fluid
• Clean blood is then returned to the patient's body
• It works on the same principle as kidneys - selective diffusion across a semipermeable membrane

When is dialysis needed? Dialysis is needed when both kidneys are severely damaged or have stopped functioning (kidney failure). Some patients may need dialysis regularly until a kidney transplant is possible.

Unlike animals, plants do not have special excretory organs. They use different methods to get rid of waste products.

Methods of excretion in plants:

• Gaseous exchange: Carbon dioxide produced during respiration is used as a raw material for photosynthesis. Similarly, oxygen produced during photosynthesis is used for respiration. So plants reuse their waste gases.
• Storage in vacuoles: Some waste products are stored in cell vacuoles
• Storage in leaves and bark: Some waste organic compounds are deposited in leaves, bark, and other parts as resin, gum, or latex
• Leaf fall: When old leaves fall, the waste products stored in them are also removed
• Transpiration: Excess water is removed through transpiration via stomata

Besides kidneys, the human body has other organs that help in excretion:

1. Sweat Glands (Skin):

• Sweat glands are present in the skin all over the body
• They produce sweat which contains water, salts, and a small amount of urea
• Sweating helps remove waste products and also cools the body
• When sweat evaporates from the skin surface, it takes heat from the body, producing a cooling effect

2. Lungs:

• Lungs excrete carbon dioxide and some water vapour with every breath we exhale

3. Liver:

• The liver breaks down old and damaged red blood cells
• It produces bile which contains waste products

Note: Excretion is not the same as egestion. Excretion is the removal of metabolic waste products, while egestion is the removal of undigested food (faeces).