Living things: cells, systems, and heredity (grade 7) · lesson

Photosynthesis

💡 Plants use light energy to turn carbon dioxide and water into sugar and oxygen.

Photosynthesis happens in chloroplasts, the green parts of plant cells.

Leaves take in carbon dioxide from the air. Roots take in water. Using light energy, the plant turns them into glucose, a sugar, and gives off oxygen.

The carbon in the sugar comes from the air. Plants use the sugar to build their bodies. So most of a tree's wood is made from carbon dioxide, not from soil.

🧠 Let's work it out

Use bubbles as evidence.
A water plant gives off oxygen bubbles.
Closer to a lamp, it makes more bubbles.

What do you think comes next?

photosynthesis: how plants use light to make sugar from carbon dioxide and water
glucose: a sugar that stores energy
chloroplast: the green part of a plant cell where photosynthesis happens

🔗 Khan Academy: Matter and energy in organisms · Khan Academy ↗

Cellular respiration

💡 Cells break down sugar with oxygen to release energy, giving off carbon dioxide and water.

Your cells need energy to work. They get it by breaking down sugar from food. This is cellular respiration.

Respiration uses glucose and oxygen. It releases energy and makes carbon dioxide and water. It is almost the reverse of photosynthesis.

Working muscles need more energy. So during a race, you breathe faster to bring in more oxygen.

🧠 Let's work it out

Trace energy from sun to muscle.
A plant captures light and stores it in sugar.
You eat the plant.
Your cells break down the sugar and release the energy.

What do you think comes next?

cellular respiration: how cells break down sugar with oxygen to release energy

Genes and environment shape growth

💡 How an organism grows depends on both its genes and its environment.

Genes are instructions passed from parents. They set limits on how big a living thing can grow.

The environment matters too. Light, food, water, and space all affect growth.

Scientists test this by keeping one factor the same and changing the other.

🧠 Let's work it out

Find what was kept the same.
Plant cuttings with the same genes grew taller in sun than in shade.
The genes matched, so the light made the difference.
Two chicken breeds with the same food and space grew to different sizes.
The environment matched, so genes made the difference.

What do you think comes next?

gene: an instruction for a trait, passed from parent to offspring
environment: everything around a living thing

Help with reproduction

💡 Special structures and behaviors raise a living thing's chances of reproducing.

Many flowers have bright petals and sweet nectar. Bees and birds visit for the nectar and carry pollen from flower to flower. That lets seeds form.

Animals have behaviors that help too. In spring, many male birds sing and show bright feathers to attract a mate.

🧠 Let's work it out

Ask who the trait is for.
Nectar is not food for the plant.
It is a reward for visitors.
The visitors carry pollen, and that helps the plant make seeds.

What do you think comes next?

pollen: a powder from flowers needed to make seeds
reproduce: to make offspring