Biology (Topic 1) Flashcards
(11 cards)
It is easier to view cells using the low power objective lens first. Give one reason why.
Any one from:
- biggest / widest field of view
- easier to focus
To focus the image the objective lens should be moved away from the stage.
Give one reason why the objective lens should not be moved towards the stage.
To avoid damage to the lens / slide.
How do you prepare a slide to view onion cells?
- Start with a clean microscope SLIDE.
- Add a single DROP OF WATER to the slide.
- Carefully cut an onion and separate it into layers.
- With TWEEZERS, peel off a piece of the EPIDERMAL tissue and place it onto the drop of water on your slide.
- Add a drop of IODINE SOLUTION as a stain to highlight cell features.
- Place a COVER SLIP over the specimen carefully to avoid air bubbles which can obstruct the view.
Once you have prepared your slide, how do you use a light microscope?
- Secure the slide on the stage of the microscope.
- Begin with the LOWEST-POWERED OBJECTIVE LENS.
- Adjust the COARSE ADJUSTMENT KNOB to bring the stage close to the lens without it touching.
- Look through the EYEPIECE and use the COARSE ADJUSTMENT KNOB to find the focus.
- Fine-tune the focus with the FINE ADJUSTMENT KNOB for a clear image.
- For greater detail, switch to a higher-powered objective lens and refocus.
How do you draw microscopical observations?
- Draw what you observe with a PENCIL.
- Ensure the drawing occupies at least half of the space provided.
- Use clear, UNBROKEN LINES, and avoid coloring or shading.
- Draw cells proportionally, labelling important features like the nucleus or chloroplasts with straight lines.
- Include a TITLE and the MAGNIFICATION LEVEL.
How do you calculate magnification?
Magnification = Image Size / Actual Size
Parts of a Microscope:
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Give one way that the palisade layer is adapted for photosynthesis.
Any one from:
- Its cells contain many chloroplasts.
- Positioned nearest to the light.
- At the top of the leaf.
- Cells are closely packed.
How is nutrient absorption maximised in the small intestine?
- The SMALL INTESTINE maximises absorption efficiency through structures called VILLI.
- Villi are tiny projections that significantly expand the surface area available for nutrient absorption into the bloodstream.
- They consist of a SINGLE LAYER OF SURFACE CELLS and a rich supply of BLOOD CAPILLARIES to facilitate quick absorption of digested nutrients.
How is gas exchange maximised in the lungs?
- The LUNGS are responsible for the crucial exchange of gases: OXYGEN is taken in, and CARBON DIOXIDE is expelled.
- This exchange occurs in millions of tiny air sacs called ALVEOLI.
- Alveoli have a HUGE SURFACE AREA — around 75 square metres in humans — to increase the efficiency of gas exchange.
- They possess a MOIST LINING for dissolving gases, which aids in the diffusion process.
- Their WALLS are extremely THIN to minimize the distance gases must diffuse.
- Alveoli are surrounded by a dense CAPILLARY NETWORK, ensuring a rich blood supply and rapid gas exchange.
Explain why a multicellular organism cannot absorb all the nutrients it needs by diffusion through its outer surface.
Multicellular organisms cannot solely rely on diffusion for nutrient absorption due to their larger size and lower surface area-to-volume ratio compared to single-celled organisms. As the distance from the outer surface increases, diffusion becomes inefficient, and specialized structures are necessary to assist in nutrient absorption. This limitation highlights the need for multicellular organisms to develop systems such as circulatory and digestive systems to ensure adequate nutrient supply to their cells.
