Bertopia

Biology Essentials

Why living things work the way they do

Biology Essentials is a Bertopia flashcard pack of 64 cards: why living things work the way they do. It covers cells and membranes; energy: photosynthesis and respiration; DNA, genes and inheritance; evolution and ecology; organ systems.

Sample cards

What does cell theory say about where cells come from?
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Answer

All cells arise from pre-existing cells
Cell theory says all living things are made of cells, the cell is the basic unit of life, and new cells come from existing cells by division. Viruses are not cells; they cannot reproduce without a host.
What are the inputs of photosynthesis?
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Answer

Carbon dioxide, water and light energy
Plants use light energy to convert CO2 and water into glucose, releasing oxygen as a by-product. Glucose and oxygen are the inputs of aerobic respiration.
In DNA, adenine pairs with which base?
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Answer

Thymine
A pairs with T via two hydrogen bonds, and G pairs with C via three. Uracil replaces thymine in RNA.
What must a population have for natural selection to occur?
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Answer

Heritable variation that affects survival or reproduction
Selection acts on inherited variation: individuals with traits that improve reproduction leave more offspring, so those alleles become more common. Effort during life is not inherited.
Why are alveoli efficient at gas exchange?
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Answer

Huge surface area, thin walls and a rich blood supply
Millions of alveoli give a large area, walls one cell thick give a short diffusion distance, and capillaries keep the concentration gradient steep.
What is the key structural difference between prokaryotic and eukaryotic cells?
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Answer

Prokaryotes lack a membrane-bound nucleus
Bacteria and archaea keep their DNA in a nucleoid region with no surrounding membrane. They still have DNA, a plasma membrane and ribosomes that make proteins.

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