Characteristics of living things

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.

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 head of lettuce when it dehydrates).

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.

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 toward the Sun.

A cat that hears a noise turns its ears toward 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.

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.

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

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.

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.

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

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.

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.

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 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.

An unincubated egg, a dry seed, a snowflake, and the flame of a candle: make 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.

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?

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

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.