Before starting with Class 7 Science Chapter 7 i.e. ‘Transportation in Animals and Plants’, I am hoping that you have completed Chapter 6 of the 7th class. If not, then you can go through its Notes and NCERT Exercise Solutions whose links have been provided below. ⤵️
Table of Content
Introduction
In the previous chapters, we have learned that all living organisms need food, water and air for their survival. They need to transport all these materials to all of their parts.
- Food that is produced mainly in the leaves by the process of photosynthesis needs to be transported to every single cell of the plant.
- Water that is absorbed by the plant roots needs to be transported to the leaves.
- The oxygen that we inhale needs to be transported to every single living cell.
- Waste that our cells produce through various life processes needs to be get rid of.
But how does all this take place in living organisms?
Well, that’s what we are going to learn about in this chapter.
Circulatory System
The human circulatory system also known as the cardiovascular system is made up of the human heart and blood vessels that circulate blood throughout the body.
1. Blood
Have you ever gotten your knees scraped while playing on a field or gotten your fingers cut while using a knife?
A red colour liquid starts to come out of the wound. This red-coloured liquid is called ‘Blood‘ that flows in our vessels. But after some time it forms a dark-coloured clot on the wound to seal it.
It transports substances like nutrients absorbed by the small intestine, oxygen inhaled by the lungs, waste generated by various tissues and organs, etc.
Blood is mainly composed of entities:
- Plasma
- Red Blood Cells
- White Blood Cells
- Platelets
PLASMA:
- It is the liquid part of the blood.
- It makes up about 55% of the blood volume and it carries the various types of blood cells, nutrients, waste products, etc.
RED BLOOD CELLs (RBCs):
- They are bright red in colour because they contain a special pigment called Haemoglobin.
- Haemoglobin binds with oxygen and transports it to all parts of the body.
- It’s the haemoglobin that makes our blood appear red in colour.
WHITE BLOOD CELLs (WBCs):
- These cells are colourless actually.
- They help our body to fight against germs and infections.
PLATELETS:
- These cells are involved in the clotting of blood, to stop the continuous flow of blood out of the wounds.
2. Blood Vessels
Blood vessels are the network of tubes through which blood is pumped around the body.
There are mainly two types of blood vessels that are present in humans:
- Arteries
- Veins
ARTERIES:
- They are thick and elastic-walled tubes.
- They carry oxygen-rich blood from the heart to the various parts of the body.
- The blood flow in them is very rapid and at high pressure.
VEINS:
- They carry the deoxygenated or carbon-dioxide-rich blood from all parts of the body back to the heart.
- Their walls are thin.
- There are valves present in the veins that allow blood to only flow in one direction i.e towards the heart
CAPILLARIES*
On reaching the tissues, the arteries divide further into very fine tubes called the capillaries and these capillaries join to form veins.
SPECIAL OR EXCEPTIONAL ARTERIES AND VEINS*
Till now we have learnt that the arteries carry the oxygenated blood whereas the veins carry the deoxygenated blood but that’s not always the case. There are a few exceptions to this:
- Pulmonary Artery: carries the deoxygenated blood from the heart to the lungs.
- Pulmonary Vein: carries the oxygenated blood from the lungs to the heart.
Pulse & Pulse Rate
Put the middle and the index finger of your right hand on the inner side of your left wrist. Then you will be able to feel throbbing.
This throbbing is called the pulse and it is due to the blood flowing in the arteries.
And, the number of pulse beats per minute is called the pulse rate. A resting person has a pulse rate of 72-80 beats per minute.
Pulse rate of a person can vary according to the time of the day, health issues, physical exercise, etc.
3. Heart
The heart is a muscular organ that is situated in your chest cavity with its lower tip slightly tilted towards the left. It beats continuously till we live and acts as a pump for the transport of blood in your body.
It is roughly the size of your left-hand fist.
A human heart has 4 chambers that prevent the mixing up of oxygenated blood with deoxygenated blood.
The upper two chambers of the heart are called the atria (singular: atrium) and the lower two chambers of the heart are called ventricles.
The left and right chambers are separated by a septum or partition that prevents the mixing of oxygenated blood in the left chambers with the deoxygenated blood in the right chambers.
Blood flows in a double circulation manner in the human body:
- The first circulation is between the heart-lungs-heart (pulmonary circuit).
- Second circulation is between the heart-body-heart (systemic circuit).
Here is a video (© Biology Bugbears YouTube Channel) that explains this double circulation in a short and comprehensive manner: https://www.youtube.com/watch?v=YK5iCvUy0RQ
Did You Know?
The English physician, William Harvey discovered the blood circulation system.
Heartbeat
As we learned earlier that the heart is a muscular organ means the walls of the chambers of heart is made up of muscles. These muscles contract and relax rhythmically.
And, this rhythmic contraction followed by its relaxation constitute a heartbeat. You can feel your heart beating in your chest cavity just by placing your hand on the left side of your chest.
Doctors use a special instrument to feel heartbeats called a stethoscope. This device amplifies the sound of your beats.
- It consists of a chest piece that has a sensitive diaphragm.
- Two earpieces for listening.
- A rubber tube to carry the amplified sound from the chest piece to the earpieces.
Doctors make their diagnoses about your heart by listening through a stethoscope.
Each heartbeat generates one pulse in the arteries and the pulse rate per minute indicates the rate of heartbeat.
Did You Know?
The animals like Hydra and sponges do not possess any circulatory system.
The water in which they live brings food and oxygen as it enters their body. The water carries away waste materials and carbon dioxide as it moves out. Thus, these animals don’t need circulatory fluid like blood, etc.
Excretion in Animals
When our cells perform their functions then certain waste products are produced. These waste products can be toxic and hence need to be removed from the body.
The removal of wastes produced in the cells of living organisms is known as excretion. The body parts (organs, tissues, etc.) involved in this process form the excretory organs.
Some of the common examples of excretion in humans are:
- Exhaling or breathing out of the carbon dioxide gas.
- Passing of stool (faeces) through the anus also known as egestion.
- Passing of urine.
- Sweating, etc.
Excretory System in Humans
The waste material that is produced by our cells gets mixed up in our blood and it needs to be removed from time to time. Our body has a special mechanism and organs to do this filtration. The blood capillaries in our kidneys do this filtration of blood.
When blood reaches our kidneys it contains both the waste materials and the useful materials mixed up in it. So, the kidneys retain the useful materials to absorb them back in the blood and remove the waste material dissolved in water as urine.
From the kidneys, the urine goes into the urinary bladder through tube-like structures called ureters. The urine is stored in the bladder for the time being and then it is passed through the urinary opening at the end of a muscular tube called the urethra.
So, the human excretory system is composed of:
- Kidneys
- Ureters
- Urinary bladder
- Urethra
A healthy human being normally pass about 1-1.8 L of urine in one day.
Human urine mainly consists of:
- 95% Water
- 2.5% Urea
- 2.5% other waste products
During the summer and heavy workout we sweat a lot. Our sweat mainly consists of water and salts. Sweat keeps our body cool by evaporation.
The way in which the waste products are removed from our bodies depends upon the availability of water in their habitat.
- Aquatic animal waste is rich in ammonia which directly dissolves in water.
- Reptiles (snakes, lizards, etc.) and birds excrete a semi-solid and white-coloured compound rich in uric acid.
- The major excretory product in humans is urea.
KIDNEY FAILURE:
Sometimes due to some illness or injury, our kidneys stop working, as a result of this kidney failure the waste products start to accumulate in our blood which can be lethal for a person’s survival. So, we need to artificially filter our blood with the help of an artificial kidney or machine called a dialysis machine, and this process of artificial blood filtration is called dialysis.
Transport of Substances in Plants
In the previous chapters, we have learned that in the plants
- The food is prepared by the leaves and later this food is transported to all parts of a plant.
- And, the water and minerals are absorbed by the roots and made available to various parts of a plant.
But the question is, how does this transportation of food, water & minerals take place in a plant?
Let’s solve this mystery.
Transport of Water and Mineral
The plant absorbs water & minerals through its roots and the roots of a plant have various minute root hairs.
These root hairs increase the surface area of the root for the absorption of water and minerals present in the soil.
Once the root hairs absorb the water, it is transported to various parts of a plant via the pipe-like vessels. These vessels are made up of special types of cells forming the vascular tissue.
A tissue is basically a group of cells that performs specialized function(s) in an organism.
The xylem is the vascular tissue that transports water and minerals in plants. The xylem forms a continuous network of channels that connects the roots to the leaves through the stem and branches and thus transports the water to the entire plant.
The food that is synthesized in the leaves of a plant is transported to the entire plant by the vascular tissue known as phloem.
It is the vascular tissues (xylem & phloem) that transport substances in plants from one location to another.
Transpiration
In the 6th class, we learnt about the concept of transpiration and transpirational pull.
Transpiration is the release of water vapours into the atmosphere by leaves. A plant loses a large amount of water this way.
A plant does this to generate a transpirational pull for the upward water movement into the plant.
To understand this concept in depth we can perform a simple activity at home and draw analogies from it:
ACTIVITY:
- Take a glass filled with water and a transparent straw.
- Dip one end of the straw into the water.
- Does the water start to come out of the other end of the straw?
- Of course not, because of the gravity the water will not automatically start to come out of the other end. We need to exert a pull that is stronger than gravity for the water to start coming out of the other end of the straw.
- For that, we will now suck the water from the other end of the straw.
- Does the water start to come out of the other end of the straw via sucking?
ANALOGIES:
- Glass of water :: Water present in the ground
- Straw :: Roots and the xylem vessels of a plant
- Sucking :: Transpirational pull
Just like sucking generates an upward pull of water, the transpirational loss of water generates an upward pull of water that transports the water from the ground to the tip of the leaves.
Other than generating the transpirational pull, transpiration also cools down the plant.
Conclusion
Did you know that thousands of people die each year due to the unavailability of blood for transfusion? Voluntary blood donation is a noble practice that can save these precious lives. Blood can be donated at hospitals and other places that are authorized by the Govt. of India. Donated blood is stored with special care in the Blood Banks and later this blood is transfused to the patients that need it the most.
For more information about blood donation visit your nearby PHC (Public Health Centre) or Government hospitals.
You will get to know about the process of transfusion, and blood groups in the higher classes.
Credits & References
- Class 7th Science NCERT Textbook
- Image by freepik
- Image by Clker-Free-Vector-Images from Pixabay
- https://www.medicalnewstoday.com/articles/180986#definition
- Image by freepik
- https://www.youtube.com/@BiologyBugbears
- Image by OpenClipart-Vectors from Pixabay
- Image by brgfx on Freepik
- Image by freepik
- Image by brgfx on Freepik
- Image by Anil sharma from Pixabay
- Image by Pavan Prasad from Pixabay
- Image by Daniel Franco from Pixabay
- Image by Beto from Pixabay
- https://my.clevelandclinic.org/health/treatments/14618-dialysis
- Image by brgfx on Freepik
- Image by brgfx on Freepik
- Image by brgfx on Freepik
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