Exercises: Characteristics of living things

Look at the diagram: a living thing carries out three life processes, labeled with letters A, B, and C. Name the life process represented by each letter, briefly describe what it involves, and give an example of an animal or plant carrying it out.

List the four most abundant bioelements in living things and explain what it means that all living things share a common chemical composition.

An earthworm, an oak tree, and a mushroom have very different sizes and shapes. State at least three shared characteristics that prove all three are living things.

Name the three life processes of living things and give an example from your own life today for each one.

Classify these items as living things or non-living matter, justifying one of the cases: a stone, a mushroom, a cloud, a firefly, the water of a river, and the moss on a wall.

Water is the most abundant substance in most living things. Explain what this statement means and give two examples that show it (for example, what approximate percentage of the human body is water, or what happens to a lettuce when it dehydrates).

State which life process each of these belongs to: a plant makes its food using light, a rabbit flees when it hears a fox, a pair of storks raises their chicks, and a sunflower turns its flower towards the Sun.

Fire "grows", moves, "feeds" on firewood, and can "reproduce" in sparks that light another fire. Explain why, even so, nobody considers it a living thing.

Is a virus a living thing? Justify your answer considering which life processes it can carry out and which it cannot (viruses can only replicate when inside a host cell).

A salt crystal "grows" if more salt is added to its solution. Explain why this growth does not make the crystal a living thing, pointing out at least two differences compared to the growth of a plant.

A cat that hears a noise turns its ears towards it and freezes. Identify the stimulus and the response, state which life process it is carrying out, and explain why this is useful to the cat.

Identify the stimulus and the response in each case, and reason in which of them a nervous system is involved: (a) a seed germinates when spring temperatures rise; (b) you pull your hand away when you touch a hot frying pan, without thinking.

Many desert animals only come out of their burrows at night. Explain which life process this behaviour involves and what advantage it brings for surviving in that environment.

A bacterium reproduces by dividing into two identical cells, whereas a dog has puppies after mating. Explain what both forms of reproduction have in common and one important difference between them.

A tadpole turns into a frog: it changes shape, loses its tail, and develops legs and lungs. Explain the difference between growing and developing using this example.

All living things need energy to live. Explain where a plant gets it from and where an animal gets it from, and name two activities in your daily life that you can only do thanks to the energy from food.

An archaeology team has found wheat grains in a sealed jar dating back 3000 years. A member of the team states: "They are completely dry, they neither move nor grow, so they are inert matter, exactly like grains of sand."

1. a) Design an experimental test to find out whether these seeds are still alive without having to wait weeks to see if a complete plant develops.
2. b) Several seeds are placed in an airtight jar with sensors at 20 °C, and it is found that the oxygen level drops from 20.9 % to 20.4 % in 48 hours, while carbon dioxide increases by 0.5 %. Interpret this result: what life process is being detected at the cellular level and what does it prove about the dormancy state of the seeds?

A classmate makes the following statement: "Plants like the pine tree feed on soil and fertilizer exactly the same way a deer feeds by eating branches; the only difference is that the deer moves around to look for food and the pine tree does not."

1. a) Refute their statement by explaining where each of these two living organisms actually obtains matter and energy.
2. b) Predict what would happen to the mass of the deer and the biomass of the pine tree if they are enclosed together in a large transparent dome where no matter other than water enters from the outside, but sunlight does. What if we cover the dome with an opaque tarp that completely blocks light? Justify the ecological role of each in both cases.

A robot vacuum cleaner moves around the house, avoids obstacles, and returns to its dock by itself to recharge its battery. Check each characteristic of living things one by one and conclude, providing arguments, whether the robot could be considered alive.

Design a mini-investigation to test whether lentil seeds need light to germinate: hypothesis, set-up with two containers (one in a dark cupboard and one by the window), control variables, what you will observe each day, and which life process you are studying.

An unincubated egg, a dry seed, a snowflake, and the flame of a candle: draw up a table with the characteristics of living things (being made of cells, carrying out the life processes, sharing the same chemical composition) and decide, case by case, whether each one is alive, was once part of a living thing, or never was, defending each decision.

To study how the environment influences the proliferation of bread mold, four identical slices were placed in sealed containers for 6 days and the percentage of invaded surface was measured:

• Container 1 (dry bread at 20 °C): 0 % mold.

• Container 2 (bread with 5 ml of water at 4 °C in a refrigerator): 2.5 % mold.

• Container 3 (bread with 5 ml of water at 20 °C): 85.0 % mold.

• Container 4 (bread submerged in 30 ml of water at 20 °C): 8.0 % mold.

1. a) From these data, deduce which two environmental conditions mold needs to successfully carry out its nutrition and reproduction. Why was its growth in container 4 so low despite having moisture and a warm temperature?
2. b) A student states: "The mold in container 3 arose by spontaneous generation from the moist bread." Refute their statement based on cell theory and explain how the mold actually reached the slice.

If you forget to water a houseplant for two weeks, it ends up wilting. Explain which life processes are disrupted by the lack of water, in which order you think the symptoms will appear, and what this shows about the relationship between the life processes.

A space agency is analyzing three celestial bodies in the solar system to select where to send a mission in search of microorganisms:\n- Planet A: surface temperature of 450 °C, no liquid water, dense carbon dioxide atmosphere, and sulfuric acid clouds.\n- Moon B: surface temperature of -160 °C beneath an ice crust, but with a subsurface ocean of liquid water at 1.5 °C in contact with underwater hydrothermal vents.\n- Moon C: temperature of -180 °C, with large surface lakes and rivers of liquid methane, but a total absence of water.\na) Applying what you know about extremophilic bacteria on Earth and the characteristics of living things, predict with reasoned arguments on which of the three bodies it is most likely to find life. Justify your choice by ruling out the other two based on the limitations they impose on cells.\nb) Why is the presence of liquid water considered an indispensable requirement for life, whereas the lack of light or extreme temperatures do not prevent the existence of certain living things?