(2)

The air sacs in lungs are known as alveoli. The alveoli are the sites where exchange of the gases takes place. The concentration of oxygen gas in the alveoli is higher than that in the blood during inhalation, therefore it diffuses into the blood. Concentration of carbon dioxide is more in the blood than that in the alveoli during exhalation, thus it diffuses into the alveoli.

(1)

In vascular plants, xylem is a type of tissue that transports water and some nutrients from the roots to the leaves. The other type of transport tissue is phloem, which is responsible for transporting sucrose and other nutrients throughout the plant. The xylem acts as a conducting tissue to transport water and some soluble nutrients such as minerals and inorganic ions from the roots to the rest of the plant.

(3)

Kidneys are the bean shaped reddish brown paired organs in human beings. These are a part of excretory system that helps in the process of urine formation. Thus kidneys help in excretion.

(3)

Urine from the nephron is transported to the collecting duct, where it enters the ureters. Ureters open from kidney into the urinary bladder. The urinary bladder holds urine, and as the volume of urine collected increases, so does the size of the bladder. When the CNS sends a voluntary message to the bladder, the bladder muscles contract and the bladder sphincter relaxes, allowing urine to pass through the urethra.

(2)

For the experiment where $CO₂$ is given out during respiration, KOH solution or pallets are taken in a test tube and placed in the conical flask. KOH absorbs carbon dioxide and prevents it from being utilised by the plant for the process of photosynthesis.