Living Creatures: Exploring their Characteristics · Lesson 2 of 8
Life Processes and Responses
“Build a fuller picture of life through respiration, excretion, responses, reproduction and death.”
• Describe breathing as part of respiration and recognise that plants also exchange air. • Explain excretion using examples from animals and plants. • Identify a stimulus and describe how a living being responds. • Explain how reproduction maintains the continuity of a kind of living being. • Use several characteristics to revisit a living-versus-non-living classification.
Life continues even when a body is still
A person resting in a chair is not walking, but the body is still carrying out important processes. Observe a dog or cat at rest: movement of the abdomen can help you notice its breathing. Plants also carry out life processes without obvious travelling. Looking for ongoing processes is more dependable than waiting for dramatic movement.
Breathing and respiration
Count your breaths for one minute after a quiet walk, then after a run or a few dance steps. Record each count fairly. The number can change with activity, but in every case air goes into the body during inhalation and back out during exhalation. Breathing is part of respiration, a process living beings need. The experiment asks you to compare observations, not to expect everyone to obtain identical counts.
A life process involving the use of air by living beings; breathing in and out is part of it in humans and many animals.
Plants respire too. Tiny pores called stomata on the surfaces of leaves help air move in and out. A microscope demonstration can show these pores even though they are too small to inspect easily with the unaided eye. Do not decide that a plant does not respire simply because it has no nose or visibly moving chest.
Problem
A student counts 19 breaths per minute after walking and 31 after running. What does the comparison show?
- 1.Both counts are observations of the same student over the same one-minute interval.
- 2.The count increased by 31 − 19 = 12 breaths per minute after the more vigorous activity.
- 3.This supports the observation that breathing rate can change with activity; it does not mean the student was not respiring while walking.
Removing waste
Living bodies produce materials they must remove. Sweat contains water and salts, which may leave pale patches on a shirt after a hot day. Urine is another animal waste product. Plants can release excess water and minerals as droplets on leaves, as the chapter illustrates with grasses and roses. The process of removing waste products is called excretion.
The removal of waste products from a living body.
Noticing and responding to change
If you step on a thorn, you quickly pull your foot away. If you touch a hot cup unexpectedly, you move your hand. The thorn and the hot surface are stimuli: events that prompt a response. Your movement away is the response. Separating the cause from the action makes the relationship clear.
Something or an event that prompts a living being to respond; the plural is stimuli.
Plants respond too. Touch-me-not folds its leaves after being touched. Leaves of some trees, including amla, come together after sunset. In these examples, touch or the change around sunset is linked with the change in leaf position. Later, we will see seedlings responding through their direction of growth.
Problem
A touch-me-not leaf folds when a child gently touches it. Identify the two parts of this observation.
- 1.The touch is the stimulus: the event that prompts a change.
- 2.Folding of the leaves is the response.
- 3.The plant stays rooted, so the example also shows why movement need not mean travel.
New generations and the end of a life
Cats and dogs can have young; a plant can produce seeds that grow into new plants. Reproduction is the production of new ones of a living kind. It allows that kind to continue across generations. A chair or electric bulb does not produce a younger chair or bulb by a life process. One individual need not be producing young at every moment to be alive; reproduction describes a capacity in the life history of a kind.
The process by which living beings produce new ones of their own kind, helping life continue across generations.
An organism eventually dies. The chapter describes a living being as dead when its life activities come to an end despite having the resources it would need to remain alive. Be careful with an inactive seed or a sleeping animal: lack of visible movement at one moment does not prove death. Return to the original classification table and revise your decisions using the full set of characteristics.
A seed can be dormant, a person can be asleep, and a young organism may not yet reproduce. Classify from the pattern of life processes across its life, not from one snapshot.
Quiz
What is breathing in relation to respiration in the chapter?
Which structures help a leaf exchange air?
A person pulls a hand away from a hot cup. What is the stimulus?
Which is an example of excretion?
Why is reproduction significant for a kind of organism?
A dry seed shows no visible movement today. Which conclusion is best?
Practice Problems
- Record your breathing rate after rest, walking and brief exercise. Compare results while keeping the counting interval the same.
- Give an animal and a plant example of air exchange and explain why no visibly moving chest in a plant is misleading.
- Identify the stimulus and response in three situations, including touch-me-not and a hot object.
- Explain why sweat and urine are examples of excretion, and describe a plant example.
- Why does producing young matter to a species, and why should an individual not be called non-living merely because it is not reproducing now?
- Return to your living/non-living table from Lesson 1 and revise two initial reasons using several characteristics.
Key Takeaways
• Breathing is part of respiration; plants exchange air through stomata. • Excretion removes waste from living bodies, including plants. • A stimulus prompts a response, which may be movement of a body part. • Reproduction maintains continuity across generations, and living beings eventually die. • Use a collection of life processes over time rather than one visible action to classify life.