Science-NCERT-Class-VII, Transportation Of Materials

 

Transportation Of Materials

AIl living organisms need to transport substances from one part Lof the body to the other for their growth and development. The substances that are transported may be nutrients, waste products, messenger molecules, heat, etc.

This movement of substances within the body becomes more and more important as the size and complexity of the organism increases. Therefore, the mechanisms of transport also advance from simple diffusion to more specialised methods. In unicellular and some lower multicellular organisms, the distribution of substances can be achieved easily by means of diffusion. The cells of these organisms exchange materials directly with the environment. In higher organisms, a separate well-organised system, known as circulatory system is employed for the efficient transport of materials.

TRANSPORTATION IN PLANTS AND ANIMALS

PLANTS

Plants are living organisms and they need water, minerals, and food for their survival. The transportation of materials in flowering plants is carried out by the vascular system. It consists of conducting tissues with cells connected end-to-end, just like in pipes. There are two kinds of conducting tissues:

1.    Xylem: The roots buried deep down in the soil absorb water that is required by the leaves for photosynthesis. Xylem conducts water from the roots to the leaves. Minerals and other water-soluble nutrients are also transported along with the water. Xylem cells are thick-walled and dead.

2.    Phloem: During photosynthesis, leaves prepare food required by all parts of the plant. Phloem transports food from the leaves to the other parts of the plant. Phloem cells are thin-walled and living.

Definition-A semipermeable membrane is a membrane that selectively allows certain molecules or ions to diffuse through it.

Transportation of water and minerals

Thin root hair present in roots of plants help to absorb water and mineral salts. The hair help by increasing the surface area of the root so that more water and minerals can be absorbed. Roots absorb water with dissolved minerals from the soil through the process of osmosis. Osmosis is defined as the movement of water molecules from an area of higher concentration to an area of lower concentration across a semipermeable membrane.

Similarly, water is absorbed from the soil by plant roots through osmosis. From the roots, water enters into the xylem tissue which is the main tissue transporting water. Xylem tissues of roots, stems, branches and leaves make a continuous channel. Therefore, water enters from roots and travels to these parts of the plant.

Transpiration

Water is continuously lost from leaves through the process of transpiration. Transpiration creates a pulling force that pulls water or mineral solution up the plant. The osmosis of water and mineral salts pushes water or mineral solutions from the root of the plant. The combined effect of these pushing and pulling forces helps in the upward movement of solutions in the plants. This upward movement of sap containing water and minerals through the xylem is called ascent of sap. Xylem transports water in an upward direction only.

Significance of transpiration

(a) It creates suction pull and therefore helps in the ascent of sap.

(b) It helps the plant to get rid of excess water.

(c) It helps in regulating the temperature of plant.

Definition-The liquid that circulates in a plant, carrying food or water and minerals is known as sap.

 

Transportation of food

Food prepared by leaves is transported in a soluble form by phloem to all parts of the plant, including the roots, through a process known as Įtranslocation. The cells of phloem make transport of food possible. These cells, called sieve tubes, are arranged one above the other to form long tubes. These tubes carry food up and down throughout the plant.

 

ANIMALS

Unicellular organisms like amoeba, paramecium, and protozoa depend entirely on diffusion for the exchange of materials with their environment. Large multicellular organisms have a circulatory system dedicated to the transport of materials inside the body. A circulatory system can either be closed or open.

 

TRANSPORTATION IN HUMANS

Humans have a closed circulatory system with a four-chambered heart. Nutrients and oxygen are delivered to each and every part of the body by the circulatory system. The human circulatory system consists of blood, blood vessels, and heart.

BLOOD

Blood is a highly specialised medium of transport consisting of blood cells suspended in a fluid medium called plasma. Blood is about 7% of the human body weight and an average adult has a blood volume of about 5 litres.

(a) Plasma: Plasma is a pale yellow-coloured liquid containing 92% water. The remaining 8% liquid is mostly proteins and small amounts of other dissolved materials. Plasma carries carbon dioxide, proteins, glucose, urea, minerals and hormones.

(b) Blood cells: There are three types of blood cells:

Red Blood Cells (RBCs): RBCs are small biconcave disc-shaped cells present in large numbers. RBCs contain haemoglobin which combines with oxygen and helps in transportation of oxygen. Haemoglobin is a red-coloured pigment which gives blood its red colour.

White Blood Cells (WBCs): WBCs help the body fight diseases by destroying infectious agents. They are known as soldiers of our body. They are larger than RBCs, but are fewer in number.

Platelets: Platelets play an important role in the clotting of blood by blocking the flow of blood in case of any injury. They are small, irregular cells.

The body of a healthy person usually creates and kills 15 million red blood cells per second!

Definition-Blood which is rich in oxygen is called oxygenated blood.

 

Functions of blood

Blood helps in the distribution of many substances within the body. Some of the functions of blood are:

Blood which has low oxygen level is called deoxygenated blood.

1. Transportation of respiratory gases (carbon dioxide and oxygen) is carried out by the blood. Blood carries oxygen from the lungs to the rest of the body and delivers carbon dioxide back to lungs, which is then exhaled.

2. Nutrients obtained from digestion of food, such as glucose, amino acids, and fatty acids are supplied to the various parts of the body by the blood.

3. Removal of wastes like urea from the body takes place through the blood.

4. Blood is the messenger of the body. It carries messenger molecules from one part of the body to the other and helps in the control and coordination of the body as a whole.

5. Components of the blood help fight infections and diseases. Blood is also the carrier for medicines.

6. Blood regulates body temperature.

BLOOD VESSELS

Blood is transported in the body through special tubes called blood vessels. There are three kinds of blood vessels:

1. Arteries: Arteries are thick-walled blood vessels which carry blood away from the heart to different parts of the body. Arteries carry oxygenated blood. The only exception is the pulmonary artery which carries deoxygenated blood from the heart to the lungs. The thick walls of arteries enable them to carry blood pumped with high pressure.

2. Veins: Veins are thin-walled blood vessels which transport blood towards the heart. They carry deoxygenated blood. The only exception is the pulmonary vein which carries oxygenated blood from the lungs to the heart. Veins contain valves which allow blood to flow only towards heart.

3. Capillaries: Arteries and veins branch into a network of extremely thin blood vessels to penetrate various tissues in the body. These fine vessels, which allow easy exchange of nutrients, gases and other materials, are called capillaries.

 

The differences between arteries and veins, in terms of structure and functions are:

Arteries

1. Arteries carry blood away from the heart.

2. Arteries transport oxygenated blood (Exception: pulmonary artery).

3. Arteries have thick walls.

4. Arteries are present deep under the skin.

5. The arterial walls are smooth, with no valves.

6. Blood moves with high pressure along the arteries.

Veins

1. Veins carry blood towards the heart.

2. Veins carry deoxygenated blood (Exception: pulmonary vein).

3. Veins have thin walls.

4. Veins are superficial and can be seen under the skin.

5. Valves are present along the walls of veins.

6. The blood is not under high pressure in veins.

HEART

The heart is a cone-shaped muscular organ. Its size is about as big as a fist. It lies between the lungs, in the protective enclosure of the rib cage. It is placed between the lungs, tilting slightly more towards the left.

The human heart has four chambers, the left and right atria (singular: atrium), and the left and right ventricles. Blood flows from the upper chambers, or atria, to the lower two chambers, the ventricles. The ventricles then pump the blood into the arteries to carry to the different parts of the body. Atria are smaller and thin-walled, whereas ventricles are bigger and have thicker walls. This is because atria receive blood, whereas ventricles have to pump blood.

Functions of the heart

The human heart beats approximately 70 times per minute with a 'lub-dub' sound. It beats rhythmically and continuously in cycles of contraction and relaxation and pumps blood.

(a) The right atrium receives deoxygenated blood from various body parts and pumps the blood to the right ventricle. From the right ventricle, the blood is sent to the lungs through the pulmonary artery for oxygenation.

(b) From the lungs, oxygenated blood returns to the left atrium through the pulmonary vein. The blood is then sent to the left ventricle. When the left ventricle contracts, the blood is pumped into the artery and distributed to various organs.

There is no mixing of oxygenated and deoxygenated blood in the heart because of a partition called septum. This partition completely separates the left and the right sides of the heart. The heart has a number of valves that allow blood to flow in one direction only.

Pulse rate

Each time the ventricles in the heart contract, a pulse or wave effect is felt due to expansion. The artery expands to accommodate the pressurised blood pumped into it. It recoils immediately as the pressure eases. Since the pulse is a result of ventricular contraction, the rate of pulse is exactly the same as the heartbeat.

Pulse rate can be checked at the wrist of any individual by keeping the two middle fingers across the wrist. A watch-like ticking can be felt at the wrist. This is the pulse.

Definition- A stethoscope is a medical device used to listen to the internal sounds of the body.

You will notice that the pulse rate is higher after exercise. When we exercise, body muscles require more energy. This energy is provided by the oxidation of glucose molecules. This causes the ventricles to pump blood faster as the demand of oxygen rises in the body during exercise.

Stethoscope-You must be familiar with a stethoscope which is often seen hanging around a doctor's neck. The rate of a heartbeat can be measured directly or with the help of a stethoscope. We can hear the sound of the heart, flow of blood in arteries and veins, etc., with the help of stethoscope. A stethoscope helps a doctor to check the functioning of our heart.

 

EXCRETION IN PLANTS AND ANIMALS

The life processes which take place inside the body, such as digestion, respiration, transportation, etc., produce some waste products along with the useful products required by the body.

The energy and nutritional requirements of an organism can vary. The body may not be able to use the entire amount of food ingested. Also, the food taken may have some components which cannot be utilized. For example, humans cannot digest fibers present in vegetables. All such components which are not usable or not required by the body are called metabolic wastes.

Sometimes undesirable materials enter the body of an organism. For example, the food we eat may contain certain contaminants harmful for the body. The body recognizes these as foreign substances and rejects them. If these wastes and foreign materials are not removed from the body and are allowed to accumulate, they can harm an organism and cause diseases.

The process of elimination of waste products and foreign substances by an organism is called excretion. Excretion is vital for the sustenance of a living organism. Let us learn how the excretion takes place in different organisms.

Excretion in plants

Plants do not have special excretory organs.

Carbon dioxide and oxygen produced as waste materials during the processes of respiration and photosynthesis are released in the atmosphere through stomata. Some plants deposit waste organic compounds in their trunks and branches as latex, gum or resin.

Excretion in animals

The two major wastes produced by animals are carbon dioxide and nitrogenous wastes, like urea, uric acid, and ammonia. Carbon dioxide is exhaled during respiration. In smaller animals, ammonia diffuses out directly from the cells where it is formed. For example, amoeba, paramecium, hydra, and sponges eliminate ammonia directly into the surrounding water.

For bigger and more complex terrestrial organisms, elimination by diffusion would be too slow a process to be efficient. The have special and well-organized organs for excretion.

 

EXCRETION IN HUMANS

Humans use following four mechanisms for excreting wastes from the body:

1.Exhalation: Carbon dioxide is released into the air during breathing.

2.Perspiration: Perspiration or sweating is the loss of watery fluid containing urea and salt from the surface of the skin. The primary purpose of sweating is to keep the body cool but it also helps in the elimination of some amount of urea from the body.

3. Defecation: Undigested food is egested from the alimentary canal as solid or semi-solid waste in the from of faces. The process of egestion is known as defecation.

4. Urination: Urea is mainly excreted through urine, which is 95% water, 2.5% urea and 2.5% other metabolic waste products.

 

HUNGRY BRIANS

The composition of urine stays more or less constant except during diseases. For example, glucose appears in urine only if a person develops diabetes. In normal conditions, glucose is absent from urine. Diabetes is a condition in which sugar assimilation by the body becomes affected.

THE URINARY SYSTEM

The human urinary system helps in the excretion of nitrogenous wastes in the form of urine from the body. It consists of the following organs:

1. Kidneys: Kidneys are a pair of small bean-shaped organs which filter blood to remove urea and other wastes along with excess water. Each kidney consists of millions of nephrons which help in filtering blood. Nephrons are coiled tubes with a cup-shaped funnel in which the process of filtration takes place. The nephrons are surrounded by a network of capillaries. Waste, in the form of urine, is filtered out through the funnel. The urine collected by nephrons moves into two long tubes, one from each kidney, known as ureters.

2. Ureters: Ureters are a pair of tubes which pass the urine formed in the kidneys to the urinary bladder.

 

3. Urinary bladder: The urinary bladder is a small muscular balloon like organ where urine is stored before being expelled out through the urethra. It swells up when full of urine. It shrinks in size after urine is expelled out.

4. Urethra: Urethra is the tube which allows the passage of urine. A healthy human being passes about 1.5 to 2.5 litres of urine every day.

The daily requirement of water of an adult human, to flush out urea from the body and to keep its concentration in the body below harmful level, is 2-3 litres.

Dialysis-When the function of the kidneys is affected due to some disease, we need to employ an artificial system to perform the work of the kidneys. The waste and excess water from the blood is removed by the process of dialysis. Dialysis works on the principle of selective diffusion of molecules across a semipermeable membrane, just like natural kidneys. In this, the circulating blood is filtered in an apparatus that works as an artificial kidney.

 

Extra facts- A disease may damage the kidneys so severely that they totally lose their function and this can lead to total renal failure. Under such conditions, a kidney is obtained from another person (dead/living) and transplanted into the patient. If the body of the patient accepts the transplanted kidney, it may last for 10-15 years.

NEW TERMS

• Transpirational pull: Pull exerted on the water column in the xylem vessel as a result of transpiration (loss of water) from the surface of the leaf.
• Vascular system: Network of tubes which transports material in plants.
• Xylem: Thick-walled cells that conduct water from roots to leaves of plants.
• Phloem: Thin-walled cells that transport food from leaves to other parts of plants.
• Osmosis: Movement of water molecules from an area of higher concentration to the area of lower concentration.
• Translocation: Process by which food prepared by plants is transported in a soluble form to all parts of the plant, including the roots.
• Plasma: Fluid part of the blood minus the blood cells.
• Platelets: Small, irregular cells that block the flow of blood in case of injuries.
• Atria: Two upper chambers of the human heart.
• Ventricles: Two lower chambers of the human heart.
• Stethoscope: Medical device used to listen to internal sounds of the body.
• Nephron: Coiled tubes with cup-shaped funnels found in the kidney to filter waste.
• Urinary bladder: Small, muscular, balloon-like organ which swells up when full of urine.
• Urethra: Tube that allows passage of urine.

 

Exercise- Transportation & Excretion in Plants and Animals

1. All living organisms need transportation mainly for:

A. Movement
B. Growth and development
C. Reproduction only
D. Protection

Answer: B
Explanation: Transport supplies nutrients, removes wastes, and supports growth.

 

2. Which of the following is NOT transported in organisms?

A. Nutrients
B. Waste products
C. Messenger molecules
D. DNA

Answer: D
Explanation: DNA is not transported as a circulating substance.

 

3. As organism size increases, transport becomes:

A. Less important
B. Unnecessary
C. More important
D. Random

Answer: C
Explanation: Larger organisms require efficient transport systems.

 

4. Transport in unicellular organisms occurs mainly by:

A. Circulatory system
B. Osmosis
C. Diffusion
D. Active transport

Answer: C
Explanation: Cells exchange materials directly with environment.

 

5. Higher organisms use a specialized transport system called:

A. Digestive system
B. Respiratory system
C. Circulatory system
D. Excretory system

Answer: C
Explanation: Circulatory system ensures efficient transport.

 

6. Transport system in flowering plants is called:

A. Root system
B. Shoot system
C. Vascular system
D. Epidermal system

Answer: C
Explanation: Vascular system transports water and food.

 

7. Conducting tissues in plants are:

A. Cortex and pith
B. Xylem and phloem
C. Epidermis and cortex
D. Cambium and cork

Answer: B
Explanation: Xylem and phloem conduct materials.

 

8. Xylem mainly transports:

A. Food
B. Hormones
C. Water and minerals
D. Oxygen

Answer: C
Explanation: Xylem carries water upward.

 

9. Xylem cells are:

A. Thin-walled and living
B. Thick-walled and dead
C. Thin-walled and dead
D. Thick-walled and living

Answer: B
Explanation: Xylem provides strength and support.

 

10. Phloem transports:

A. Water
B. Minerals
C. Food
D. Oxygen

Answer: C
Explanation: Phloem distributes prepared food.

 

11. Phloem cells are:

A. Dead and thick-walled
B. Living and thin-walled
C. Dead and thin-walled
D. Living and thick-walled

Answer: B
Explanation: Living cells are needed for translocation.

 

12. A semipermeable membrane:

A. Allows all substances
B. Allows no substances
C. Selectively allows substances
D. Breaks easily

Answer: C
Explanation: It allows selective diffusion.

 

13. Root hairs help in absorption by:

A. Reducing surface area
B. Increasing surface area
C. Increasing pressure
D. Producing enzymes

Answer: B
Explanation: Larger surface absorbs more water.

 

14. Water absorption in roots occurs by:

A. Diffusion
B. Active transport
C. Osmosis
D. Translocation

Answer: C
Explanation: Water moves across semipermeable membrane.

 

15. Osmosis is movement of:

A. Solutes
B. Minerals
C. Water molecules
D. Gases

Answer: C
Explanation: Osmosis involves only water.

 

16. Water moves from:

A. Low to high concentration
B. High to low concentration
C. Roots to leaves directly
D. Leaves to soil

Answer: B
Explanation: Osmosis follows concentration gradient.

 

17. Xylem forms a continuous channel through:

A. Roots only
B. Leaves only
C. Stem only
D. Roots, stem and leaves

Answer: D
Explanation: Enables upward transport.

 

18. Xylem transports water:

A. Upward only
B. Downward only
C. In all directions
D. Randomly

Answer: A
Explanation: Xylem flow is unidirectional.

 

19. Loss of water from leaves is called:

A. Osmosis
B. Translocation
C. Transpiration
D. Respiration

Answer: C

20. Transpiration creates:

A. Root pressure
B. Suction pull
C. Food pressure
D. Cell pressure

Answer: B
Explanation: Helps pull water upward.

 

21. Ascent of sap is:

A. Downward movement of food
B. Upward movement of water
C. Lateral movement of gases
D. Movement of hormones

Answer: B

 

22. Significance of transpiration includes:

A. Cooling the plant
B. Removing excess water
C. Helping ascent of sap
D. All of the above

Answer: D

 

23. Sap is:

A. Blood of plants
B. Liquid carrying water or food
C. Mineral deposit
D. Cell sap only

Answer: B

 

24. Transport of food in plants is called:

A. Transpiration
B. Osmosis
C. Translocation
D. Diffusion

Answer: C

 

25. Food is transported in:

A. Xylem
B. Phloem
C. Cortex
D. Cambium

Answer: B

 

26. Sieve tubes are found in:

A. Xylem
B. Phloem
C. Roots
D. Leaves only

Answer: B

 

27. Phloem transport occurs:

A. Only upward
B. Only downward
C. Both upward and downward
D. Sideways only

Answer: C

 

TRANSPORTATION IN ANIMALS

28. Amoeba depends on ______ for transport.

A. Blood
B. Diffusion
C. Heart
D. Capillaries

Answer: B

 

29. Humans have a ______ circulatory system.

A. Open
B. Closed
C. Semi-open
D. Absent

Answer: B

 

30. Blood is:

A. A solid tissue
B. A gas
C. A transport medium
D. A hormone

Answer: C

 

31. Blood constitutes about ___ of body weight.

A. 5%
B. 7%
C. 10%
D. 15%

Answer: B

 

32. Average blood volume in adults is:

A. 2 litres
B. 3 litres
C. 5 litres
D. 8 litres

Answer: C

 

33. Plasma contains about:

A. 70% water
B. 80% water
C. 92% water
D. 100% water

Answer: C

 

34. Which is NOT carried by plasma?

A. Glucose
B. Hormones
C. Carbon dioxide
D. Oxygen bound to haemoglobin

Answer: D

 

35. RBCs contain:

A. Plasma
B. Platelets
C. Haemoglobin
D. Antibodies

Answer: C

 

36. RBCs are:

A. Spherical
B. Cuboidal
C. Biconcave
D. Irregular

Answer: C

 

37. WBCs help in:

A. Clotting
B. Oxygen transport
C. Fighting diseases
D. Temperature regulation

Answer: C

 

38. Platelets help in:

A. Oxygen transport
B. Immunity
C. Blood clotting
D. Nutrition

Answer: C

 

39. Oxygen-rich blood is called:

A. Deoxygenated blood
B. Venous blood
C. Oxygenated blood
D. Impure blood

Answer: C

40. Blood removes which waste?

A. Oxygen
B. Urea
C. Glucose
D. Hormones

Answer: B

 

41. Blood acts as a:

A. Digestion agent
B. Messenger
C. Excretory organ
D. Respiratory organ

Answer: B

 

42. Blood helps regulate:

A. Digestion
B. Body temperature
C. Growth only
D. Reproduction

Answer: B

 

43. Arteries carry blood:

A. Towards heart
B. Away from heart
C. In lungs only
D. To veins

Answer: B

 

44. Pulmonary artery carries:

A. Oxygenated blood
B. Deoxygenated blood
C. Mixed blood
D. Plasma only

Answer: B

 

45. Veins contain:

A. Thick walls
B. No valves
C. Valves
D. High pressure blood

Answer: C

 

46. Exchange of materials occurs in:

A. Arteries
B. Veins
C. Capillaries
D. Heart

Answer: C

 

47. Human heart has:

A. Two chambers
B. Three chambers
C. Four chambers
D. Five chambers

Answer: C

 

48. Ventricles have thicker walls because they:

A. Receive blood
B. Pump blood
C. Store blood
D. Filter blood

Answer: B

 

49. Septum prevents:

A. Clotting
B. Backflow
C. Mixing of blood
D. Pumping

Answer: C

 

50. Pulse rate equals:

A. Breathing rate
B. Heartbeat
C. Blood pressure
D. Oxygen level

Answer: B

 

 

51. Removal of metabolic waste is called:

A. Respiration
B. Egestion
C. Excretion
D. Translocation

Answer: C

 

52. Plants lack:

A. Roots
B. Vascular tissue
C. Excretory organs
D. Stomata

Answer: C

 

53. Nitrogenous waste in humans is mainly:

A. Ammonia
B. Uric acid
C. Urea
D. CO₂

Answer: C

 

54. Main excretory organ in humans:

A. Lungs
B. Skin
C. Kidneys
D. Liver

Answer: C

 

55. Functional unit of kidney is:

A. Neuron
B. Nephron
C. Alveolus
D. Glomerulus only

Answer: B

 

56. Dialysis works on principle of:

A. Diffusion
B. Active transport
C. Selective diffusion
D. Osmosis only

Answer: C

 

57. Normal urine contains glucose:

A. Always
B. Never
C. During diabetes
D. During exercise

Answer: C

 

58. Urine is about ___ % water.

A. 50
B. 70
C. 95
D. 100

Answer: C

 

59. Urinary bladder stores:

A. Blood
B. Urine
C. Urea
D. Plasma

Answer: B

60. Tube that carries urine out of body:

A. Ureter
B. Nephron
C. Urethra
D. Bladder

Answer: C