Page 100 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

5. Explain the various organs of the human excretory system.
Ans. The various organs of the human excretory system are :

Kidney
The kidneys is a pair of purplish-brown organs located below the ribs towards the

middle of the back. The kidneys remove urea from the blood through tiny filtering
units called nephrons.
When blood that contains waste is brought to the kidneys, these nephrons remove
urea, salt and excess water from the blood. The filtered waste forms a liquid called

urine, which is transported to the urinary bladder via ureters. The purified blood
returns to the circulatory system.
Ureters

The ureter is a thin muscular tube that carries urine from the kidney to the urinary
bladder. Muscles in the ureter walls keep tightening and relaxing. This forces urine
downwards and away from the kidneys.

Urinary Bladder
It is a sac-like structure and stores urine till it is expelled from the body by micturition.
Micturition is the act of expelling urine from the body. The bladder receives urine

from the kidneys through the urethra.
Urethra
This tube expels urine from the body. The urethra is shorter in females and longer
in males. In males, the urethra functions as a common path for semen that contains

sperms (reproductive cells) and urine. The opening of the urethra is guarded by
sphincter muscles that controls the opening and closing of urethra.

6. State one function of each of the following.
(a) Arteries
Ans. Arteries : Arteries are blood vessels that carry oxygen-rich blood away from the heart
to all parts of the body. They have thick, elastic walls to handle the high pressure of

the blood being pumped by the heart.
(b) Veins
Veins : Veins are blood vessels that carry oxygen-depleted blood back to the heart

from the body. They have thinner walls compared to arteries & have valves that
prevent blood from flowing backward.
Capillaries : Capillaries are the smallest blood vessels that connect arteries to veins.

Their thin walls allow for the exchange of oxygen, carbon dioxide, nutrients & waste
products between the blood & the body organs.

8. Differentiate between the following.
(a) Arteries and veins (c) Atrium and ventricle

(b) RBC and WBC (d) Xylem and phloem

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