Properties of Living Things (v2.0)

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Trait 1. Living things are made of cells

In every living thing that’s ever been known to exist, you’ll find that the organism is built of tiny units called _______. Cells are the basic units of life.

The drawing at left, drawn using an early microscope in the 1600s, shows tiny cells (each square is a cell).

On the right, you can see a rectangular cell from an aquatic (water-living) plant. The small green ellipses are parts that carry out _________________. .

Plants, animals, and fungi are made of many cells. But bacteria, yeast, and most algae consist of just _____ cell. In fact, for the first few billions of years of life on Earth, that’s all that life was: ________________ organisms.

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Trait 2: Living things are highly organized.

This means that living things, and their parts, are arranged and __________. Living things have lots of _____________ structure. They’re not randomly arranged. At any level that you look at life, from the entire organism to specific parts of organisms, all the way down to the cells and molecules that make up organisms, you see high levels of _______________.

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Trait 3: Living things are maintained by a constant flow of energy and matter.

Every day (if you’re fortunate), you eat food. That food contains chemical _________ that keeps you alive. It also provides you with the atoms that make you up. With every breath, oxygen flows into you. That flow can’t stop for more than a few minutes, or life will end.

These flows of _________ and energy into you are matched by flows of matter and energy out of you. When you exhale, you breathe out carbon dioxide. Urine removes waste products from your blood. Feces removes food you can’t digest. You’re also releasing heat into the environment.

Like you, plants are also open systems, with matter and energy flowing through them. As a plant performs photosynthesis, carbon dioxide and water flow into it. Using _________ energy from the sun, the plant makes sugars and other carbohydrates. Oxygen is released as a waste product.

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Trait 4: Living things respond to their environment

Humans, like all animals, constantly __________ to the environment. These responses might be quick __________, as is shown on the left when you touch a hot piece of metal. But these responses can also occur much more slowly. Even plants respond to their environments. that’s what happens when a vine wraps itself around a branch, or when a plant’s ________ bends so that the plant’s leaves face toward the sun.

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Trait 5: Living things maintain stable, internal environments through homeostasis

Humans can live in almost every environment imaginable, from the Saharan desert to the Alaskan tundra. But to stay alive, the conditions _________ our bodies must stay within a very narrow _________. Our body temperature has to stay very close to 37°C (98.6°F).  Levels of sugar and salt in the blood also have to be tightly regulated.

This process of regulation is called _____________. If you get too hot, you sweat. As the sweat evaporates, your body cools down. Your temperature stays right around 37°C. If your blood becomes too acidic, your kidneys adjust the blood, moving it back to the _________ level.

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Trait 6: Living things reproduce by passing on their DNA

While not every living thing _____________, every living thing is part of a species in which members of that species pass their genes on to the next _____________. In every living thing on Earth, those genes are encoded in a chemical called _______. If something has DNA and can reproduce itself, it’s almost certainly alive.

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Trait 7: Living things grow and develop

Growing means increasing in size. Developing means changing form during the course of a life.

In living things that consist of only one cell, most of what you see throughout life is _________. A small cell grows to become a full-sized adult cell, which then divides again.

In living things like human beings that consist of trillions of cells, life begins as a single, fertilized _______, which then grows and develops into an embryo, and then into a vastly ________, adult organism.

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Through evolution, species _________ over time.

A species is a group of organisms that can naturally interbreed with one another to successfully produce offspring. All humans are part of the same species. Grizzly bears and polar bears are two different species because they don’t naturally interbreed with one another.

A species is adapted to its environment. That means that the species has traits that enable it to _________ and reproduce. Some obvious adaptations are:

• The spines of a cactus which discourage animals from eating it
• The talons of an eagle which enable it to grasp its prey

The process by which species become ___________ to their environments is called natural ____________. It’s one of the most important ideas in biology, and we’ll investigate it later in this course.

[q]Drag the property of living things from the list on the right to the description that best matches that property. Be sure to choose the property that fits best.

1. A bear smells berries and moves towards the smell.
   _______________________________________
2. When it’s cold, you shiver, increasing your body temperature:
   _______________________________________
3. You start life as a fertilized egg. Then you’re a ball of cells. Then a backbone and limbs appear.
   _______________________________________
4. Plants need sunlight to perform photosynthesis:
   _______________________________________
5. If you went back in time 100,000 years, the humans you would meet would not be the same as the people who exist today.
   _______________________________________
6. Insect bodies are in three segments:
   _______________________________________
7. Humans produce sperm and egg cells in order to create offspring.
   _______________________________________
8. Looking through a microscope at plant tissue, you see small repeated, rectangular units.
   _______________________________________

[q]Drag the property of living things from the list on the right to the description that’st matches that property. Be sure to choose the property that fits best.

1. A mouse hides when it sees a cat.
   _____________________________________
2. A spider eats a fly.
   _____________________________________
3. Male blue whales mate with female blue whales
   _____________________________________
4. 8 million years ago, one species of fruit fly arrived on the Hawaiian islands. Since then, that one species of fruit fly has repeatedly split and produced new species.
   _____________________________________
5. Plants start from seeds. Soon, the seedling has a root, a stem, and leaves.
   _____________________________________
6. Different plants have predictable patterns of veins on their leaves.
   _____________________________________
7. Under a microscope, the tissue lining your inner cheek can be seen to be made of repeated, tiny units.
   _____________________________________
8. Your blood sugar goes down. Your pancreas releases a hormone that gets muscle cells to release sugar into your blood.
   _____________________________________