9th grade cells, genetics and evolution

Example

Brown fur (B) is dominant over white fur (b). Two parents with genotypes Bb and bb are crossed. What percentage of the offspring are expected to have white fur?

1. Offspring: Bb, Bb, bb, bb
2. 2 out of 4 = 50%
3. So the answer is: 50%

Answer: 50 %

Example

Mitosis or meiosis? It produces genetically different cells.

1. Meiosis makes four genetically different gametes with half the chromosomes.
2. So the answer is: meiosis

Answer: meiosis

Example

Before the Industrial Revolution most peppered moths were pale. Soot darkened tree bark, and dark moths became common. Why?

1. Dark moths survived to breed more, so the dark allele became more common.
2. So the answer is: Dark moths were better camouflaged, so fewer were eaten by birds

Answer: Dark moths were better camouflaged, so fewer were eaten by birds

Example

Where is this found: a single loop of DNA not in a nucleus?

1. Prokaryotes (bacteria) have no nucleus: their DNA is a single loop, often with extra rings called plasmids.
2. So the answer is: prokaryotic cells only

Answer: prokaryotic cells only

Example

Where are stem cells found in a plant?

1. Meristem tissue can differentiate into any plant cell type throughout the plant's life.
2. So the answer is: in meristems at the tips of roots and shoots

Answer: in meristems at the tips of roots and shoots

Example

A cell is seen with chromatids moving to opposite ends. Which stage?

1. In anaphase, spindle fibres pull the chromatids apart.
2. So the answer is: anaphase

Answer: anaphase

Example

A body cell of a cat has 38 chromosomes. It divides by mitosis. How many chromosomes are in each new cell?

1. Mitosis keeps the number the same: 38
2. So the answer is: 38

Answer: 38

Example

Why does a reaction speed up as temperature rises towards the optimum?

1. More kinetic energy means more successful collisions between enzyme and substrate.
2. So the answer is: Molecules move faster, so enzyme and substrate collide more often

Answer: Molecules move faster, so enzyme and substrate collide more often

Example

Catalase in liver broke down hydrogen peroxide and released 10 cm³ of oxygen in 20 s. What was the mean rate of reaction, in cm³/s?

1. 10 ÷ 20 = 0.5
2. So the answer is: 0.5 cm³/s

Answer: 0.5 cm³/s

Example

A couple already have three daughters. What is the probability (in %) that their next baby will be XY?

1. Each pregnancy is independent: earlier children do not change the odds.
2. So the answer is: 50 %

Answer: 50 %