Cells and organisation, Year 7: microscopes and photosynthesis：全部卡片
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- When you first look at a slide under a light microscope, which objective lens should you start with?
The lowest-power lens
提示Pick the one that gives the widest view, so the specimen is easy to find.
为什么Low magnification shows a wide area and is easy to focus. Once the specimen is centred and sharp, you switch up to a higher magnification to see detail.
- Which knob on a light microscope do you turn first to bring a specimen roughly into view?
The coarse focus knob
提示It moves the stage in big steps; the other one is only for sharpening.
为什么The coarse knob makes large movements to find the image on low power. The fine knob then makes tiny adjustments to sharpen it.
- Why is a stain such as iodine or methylene blue added to cells before they are viewed under a microscope?
It makes the cell parts easier to see
提示Think about what an unstained specimen looks like against a bright light.
为什么Light passes straight through unstained cells, so there is little contrast. A stain is taken up more strongly by some parts, such as the nucleus, which then stand out.
- A pupil looking at onion cells adds green chloroplasts to the drawing because 'plant cells have them'. Which rule of microscope drawing has been broken?
Draw only what you actually see
提示Onion bulbs grow underground, so their cells are not green.
为什么A scientific drawing is a record of an observation, not a copy of a textbook diagram. Onion bulb cells have no chloroplasts, so none should appear.
- Under a microscope, a cell has a clear box-like outline and a large central space filled with sap. Is it a plant cell or an animal cell?
A plant cell
提示Think about which kind has a rigid wall and a permanent vacuole.
为什么The box-like outline is the cell wall and the central space is the vacuole. Animal cells have neither, so they look rounder and less regular.
- Photosynthesis: carbon dioxide + water → ____ + oxygen
glucose
提示The name of one particular sugar, beginning with 'gl'.
为什么The plant builds this sugar from two simple raw materials, using energy from light. Oxygen is the other product.
- Which gas do plants take in from the air to make food by photosynthesis?
Carbon dioxide
提示You breathe out more of this gas than you breathe in.
为什么It enters the leaf through tiny pores and is one of the two raw materials. The other, water, comes up from the roots.
- Which gas is released by a plant as a product of photosynthesis?
Oxygen
提示Animals need this gas for respiration.
为什么It is made alongside glucose and leaves through the pores of the leaf. Almost all the oxygen in the air was made this way.
- Where does the energy for photosynthesis come from?
Light
提示A plant kept in a dark cupboard cannot do it.
为什么Light is absorbed by the green chlorophyll in the leaf and is used to join carbon dioxide and water into glucose.
- A tree gains hundreds of kilograms as it grows. Does most of that new material come from the soil, or from the air and water?
From the air and water
提示Look at the left-hand side of the word equation for photosynthesis.
为什么The glucose a plant builds its body from is made out of carbon dioxide and water. Only a small amount of minerals comes from the soil.
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