Week 11 · Lesson 2 General Characteristics of Living Organisms: nutrition and photosynthesis, respiration, transport, excretion, movement, growth, reproduction, sensation, adaptation · 3 lessons
2
Respiration, transport and excretion
Science Prep 1 Term 1, Unit 3: pp. 64–71
GoalDistinguish breathing from cellular respiration, and describe transport and excretion in animals and plants.
New words
cellular respiration · the release of energy from glucose and oxygen inside cellstransport · carrying substances around the body of a living thingexcretion · getting rid of waste made by the bodystomata · tiny openings in leaves that let gases and water vapour pass
Explanation
Single-celled organisms take oxygen from their surroundings. Humans use lungs, fish use gills for oxygen dissolved in water, insects use tracheal tubes, adult frogs use lungs and skin, and plants use stomata. Do not mix this up with cellular respiration. Breathing brings in oxygen. Cellular respiration happens in the mitochondria of every cell, day and night, and releases energy: glucose + oxygen gives carbon dioxide + water + energy. It is the reverse of photosynthesis. Transport: the heart pumps blood to all the cells in a closed circuit. Most arteries carry oxygen-rich blood and most veins carry oxygen-poor blood. In plants, xylem carries water and minerals up from the roots, and phloem carries food from the leaves. Excretion: the lungs remove carbon dioxide and water vapour, the kidneys remove extra water, salts and urea in urine, and the skin removes water and salts in sweat. Plants lose water vapour and carbon dioxide through stomata, which guard cells open and close. When the kidneys fail, a dialysis machine can clean the blood.
Living thing
Takes in oxygen with
human
lungs
fish
gills
insect
tracheal tubes
adult frog
lungs and skin
plant
stomata
Worked examples
The heart pumps blood in a closed circuit: to the lungs, back to the heart, round the body and back again. Blood with much oxygen is drawn in red and blood with little oxygen in blue.
breathing brings in oxygen→blood carries it to cells→mitochondria release energy→carbon dioxide and water leave
Breathing is not the same as cellular respiration. Breathing brings oxygen into the body. Blood carries it to the cells. In the mitochondria, glucose and oxygen release energy, and carbon dioxide and water leave through the lungs.
Organ
Removes
lungs
carbon dioxide, water vapour
kidneys
extra water, salts, urea
skin
water, salts (sweat)
Which organ removes which waste? The lungs remove carbon dioxide and water vapour. The kidneys make urine with extra water, salts and urea. The skin removes water and salts in sweat. In a plant, stomata let out water vapour.
Class activity
Breaths and energy. With an adult, sit quietly and count your breaths for one minute. Then step gently on the spot for one minute and count again. Say what changed and why your cells may need more oxygen when you move. Then draw a loop of boxes and arrows with photosynthesis on one side and cellular respiration on the other, and write what each one gives to the other.
Practice
1
What is the difference between breathing and cellular respiration?
Breathing brings oxygen in. Cellular respiration releases energy from glucose in the cells.
2
Do plants respire only at night? Explain.
No. Plants respire day and night, because cellular respiration goes on in every living cell.
3
What do xylem and phloem carry?
Xylem carries water and minerals up from the roots. Phloem carries food from the leaves.
4
Which organs remove urea, and which remove carbon dioxide?
The kidneys remove urea. The lungs remove carbon dioxide.
