Exam 2 - LNW lecture

Describe the process of respiration.

Cells break down food (glucose) using O₂ to release energy (ATP), water, and CO₂.

What happens if respiration occurs without enough oxygen?

Cells switch to fermentation, producing less ATP and byproducts like lactic acid (animals) or alcohol and CO₂ (yeast).

Give examples of how ATP is used in cells.

 Muscle contraction, active transport across membranes, DNA replication, protein synthesis, and cell division.

How do plant cells get energy at night?

They use cellular respiration, breaking down the sugars they made during photosynthesis.

What is the difference between photosynthesis and respiration?

Photosynthesis stores energy by converting CO₂ and water into glucose and O₂. Respiration releases that stored energy by breaking down glucose with O₂.

How is photosynthesis related to global climate change?

Plants remove CO₂ from the atmosphere, acting as carbon sinks and reducing greenhouse gas concentration.

How did cyanobacteria change Earth’s atmosphere 2.5 billion years ago?

They produced oxygen through photosynthesis, increasing atmospheric O₂ and enabling aerobic life.

How does deforestation affect the carbon cycle?

Fewer trees = less CO₂ absorbed + carbon stored in trees released → increased atmospheric CO₂ = climate warming.

What is one way to reduce CO₂ in the atmosphere and why does it work?

Planting trees or restoring ecosystems. They absorb CO₂ and store it as biomass.

Explain how carbon moves in the carbon cycle.

CO₂ atmosphere, plants,  animals, respiration returns CO₂, decomposition, fossilization, humans burn fossil fuels, CO₂ returns to atmosphere.

Give examples of carbon reservoirs/sinks.

Atmosphere, oceans, forests (biomass), fossil fuels, soil, limestone.

What is residence time?

The average time carbon stays in a reservoir before moving to another.

How do fossil fuels affect the carbon cycle?

Burning them rapidly releases stored carbon (from millions of years ago) into the atmosphere as CO₂.

Describe the structure of DNA and how information is stored.

DNA is a double helix made of base pairs (A-T, C-G). The sequence of bases stores genetic instructions.

What is DNA replication?

The process where DNA unzips and each strand is copied to make two identical DNA molecules.

What is protein synthesis?

DNA → (transcription) → mRNA → (translation by ribosome) → protein.

What is the role of mRNA?

It carries the genetic code from DNA in the nucleus to ribosomes in the cytoplasm.

What does it mean when a gene is "expressed"?

It is used to make a protein. Expression can be turned on/off depending on cell needs (gene regulation)

How can a mutation affect a protein?

A change in DNA sequence can change the amino acid sequence, altering protein structure/function.

What happens if genes are turned on at the wrong time?

It can cause diseases, such as cancer or developmental disorders.

What is epigenetics?

Chemical modifications (not changing DNA sequence) that turn genes on or off depending on the environment, development, or behavior.

Difference between autotrophs and heterotrophs?

Autotrophs make their own food using sunlight/chemicals (plants). Heterotrophs consume other organisms for energy (animals).

Why are there always more autotrophs than heterotrophs?

Energy is lost at each trophic level. Producers must supply energy for all levels above them.

Explain energy flow in a trophic pyramid.

Sun, producers, primary consumers, secondary consumers, decomposers. Only 10% of energy moves up each step.

Mitosis is?

one division, two identical cells, growth/repair.

Why does sexual reproduction create more variation than asexual reproduction?

Crossing over and independent assortment in meiosis shuffle chromosomes = genetic diversity.

Meiosis is?

two divisions, four genetically unique gametes for reproduction.

asexual offspring

clones, low diversity

sexual offspring

genetic variation, adaptation potential.