Notes Class 7 Science Chapter 7 Transportation in Animals and Plants

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Transportation in Animals and Plants

Introduction

All living organisms need food, water, and oxygen for survival. These substances must be transported to different parts of the body. Waste materials also need to be carried to parts from where they can be removed. In animals, this transport is mainly done by the circulatory system, while in plants it is done by special tissues.

7.1 Circulatory System

Blood

Blood is a fluid that flows through blood vessels. It performs several important functions:

• Transports digested food from the small intestine to all parts of the body
• Carries oxygen from the lungs to body cells
• Transports waste materials for removal from the body

Blood is made up of a liquid part called plasma in which different types of cells are suspended.

Components of Blood

1. Red Blood Cells (RBCs)
   • Contain a red pigment called haemoglobin
   • Haemoglobin binds with oxygen and transports it to all parts of the body
   • Presence of haemoglobin makes blood appear red
2. White Blood Cells (WBCs)
   • Protect the body by fighting against germs and infections
3. Platelets
   • Help in clotting of blood
   • Prevent excessive bleeding when there is a cut or injury

Blood Vessels

Blood flows through different types of blood vessels:

1. Arteries
   • Carry oxygen-rich blood from the heart to all parts of the body
   • Have thick and elastic walls because blood flows under high pressure
   • Pulse can be felt due to blood flowing in arteries
2. Veins
   • Carry carbon dioxide-rich blood from body parts back to the heart
   • Have thin walls
   • Contain valves to ensure blood flows only towards the heart
3. Capillaries
   • Very thin blood vessels formed by the division of arteries
   • Reach all tissues
   • Join together to form veins

Pulse Rate: The number of pulse beats per minute. In a resting adult, it is usually between 72–80 beats per minute.

Heart

The heart is a muscular organ that acts as a pump to circulate blood.

• Located in the chest cavity, slightly tilted towards the left
• About the size of a clenched fist

Chambers of the Heart

The heart has four chambers:

• Two upper chambers called atria (right atrium and left atrium)
• Two lower chambers called ventricles (right ventricle and left ventricle)

A partition separates the right and left sides of the heart to prevent mixing of oxygen-rich and carbon dioxide-rich blood.

Blood Circulation

• Oxygen-poor blood goes from the heart to the lungs through the pulmonary artery
• Oxygen-rich blood returns from the lungs to the heart through the pulmonary vein
• From the heart, oxygen-rich blood is pumped to the rest of the body

Heartbeat

• Heart chambers are made of muscles that contract and relax rhythmically
• One contraction and relaxation make one heartbeat
• Heartbeat continues throughout life
• A stethoscope is used by doctors to hear the heartbeat

Each heartbeat produces one pulse in the arteries. Therefore, pulse rate and heart rate are related.

Animals Without Circulatory System

Animals like sponges and Hydra do not have a circulatory system.

• Water entering their body brings food and oxygen
• Water moving out carries waste materials

7.2 Excretion in Animals

Excretion

Excretion is the process of removal of waste products produced in the cells of living organisms. These wastes are toxic and must be removed.

Human Excretory System

The excretory system in humans consists of:

• Two kidneys
• Two ureters
• One urinary bladder
• Urethra

Functioning

• Blood reaches the kidneys containing useful and waste substances
• Useful substances are reabsorbed into the blood
• Waste substances dissolved in water form urine
• Urine passes from kidneys → ureters → urinary bladder → urethra → outside the body

An adult human produces about 1–1.8 litres of urine per day.

Composition of Urine:

• 95% water
• 2.5% urea
• 2.5% other waste substances

Dialysis

If kidneys stop working due to infection or injury:

• Waste products accumulate in the blood
• Blood is filtered using an artificial kidney
• This process is called dialysis

Excretion in Other Animals

• Aquatic animals (fish): excrete ammonia which dissolves directly in water
• Birds, lizards, snakes: excrete uric acid in semi-solid form
• Humans: main excretory product is urea

Sweat

• Sweat contains water and salts
• Helps in removing salts from the body
• Evaporation of sweat cools the body

7.3 Transport of Substances in Plants

Plants need to transport water, minerals, and food to different parts of their body.

Transport of Water and Minerals

• Roots absorb water and minerals from the soil
• Root hairs increase the surface area for absorption
• Water absorbed by roots reaches leaves through special tissues

Xylem

• Vascular tissue that transports water and minerals
• Made of pipe-like vessels
• Forms a continuous network from roots to leaves

Transport of Food

• Leaves prepare food by photosynthesis
• Food must reach all parts of the plant
• Transport of food is done by phloem

Transpiration

Transpiration is the loss of water in the form of vapour from leaves through stomata.

Functions of Transpiration:

• Creates suction pull that helps water rise to great heights in tall trees
• Helps in cooling the plant