ATI TEAS: Biology Concepts
Importance ★★★★☆ · 20% (estimate)
Overview
This chapter covers life at the level of the cell. You will learn the parts of a cell and what they do, how cells divide, how DNA carries instructions to make proteins, how traits are passed from parents to children, and the basic types of microorganisms.
Each organelle has a job. The nucleus holds the DNA, mitochondria make most of the cell's energy in the form of ATP, ribosomes build proteins, and the cell membrane controls what goes in and out. Plant cells also have a cell wall and chloroplasts for photosynthesis.
Mitosis makes two identical body cells for growth and repair, while meiosis makes four cells with half the usual number of chromosomes, which become sex cells. DNA is copied into RNA in a step called transcription, and RNA is used to build a protein in a step called translation. In genetics, a dominant allele shows its trait even if only one copy is present, while a recessive trait shows only when both copies are recessive.
Key concepts
Mitochondria
Organelles that carry out cellular respiration and produce most of the cell's usable energy as ATP.
Memory tipMitochondria = the cell's power plant.
Nucleus and ribosomes
The nucleus stores DNA and controls the cell. Ribosomes read RNA instructions and assemble proteins from amino acids.
Memory tipNucleus holds the plans; ribosomes build the product.
Mitosis
Cell division that produces two daughter cells identical to the parent, each with the full set of chromosomes. Used for growth and repair.
Memory tipMitosis: 2 identical cells.
Meiosis
Cell division that makes four genetically different cells, each with half the chromosomes of the parent cell. These become sex cells: sperm in males, and in females one egg (the other cells are small polar bodies).
Memory tipMeiosis: 4 cells, half the chromosomes.
Transcription, translation
Transcription copies a gene from DNA into messenger RNA in the nucleus. Translation uses that RNA at a ribosome to build a protein.
Memory tipDNA -> RNA -> protein.
DNA base pairing
In DNA, adenine pairs with thymine and cytosine pairs with guanine. In RNA, uracil replaces thymine, so adenine pairs with uracil.
Memory tipA-T and C-G in DNA; A-U in RNA.
Dominant and recessive
A dominant allele shows its trait with just one copy. A recessive trait shows only when both alleles are recessive. A Punnett square predicts offspring combinations.
Memory tipAa x Aa gives a 3:1 ratio of dominant to recessive traits.
Often tested
- Bacteria are prokaryotes with no nucleus; human, plant, and fungal cells are eukaryotes with a nucleus.
- Viruses are not cells and need a host cell to reproduce.
- Homozygous means two matching alleles (AA or aa); heterozygous means two different alleles (Aa).
- Human body cells have 46 chromosomes; sex cells have 23.
Easy to confuse: Mitosis vs. meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth and repair | Making sex cells |
| Number of cells made | 2 | 4 |
| Chromosome number | Same as parent (46 in humans) | Half of parent (23 in humans) |
| Genetically | Identical to parent | Different from each other |
3 sample questions
Verified practice questions from this unit.
Question 1. Which organelle makes most of a cell's ATP (energy)?
- ① Ribosome
- ② Nucleus
- ③ Golgi apparatus
- ④ Mitochondrion
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Answer: ④ Mitochondrion
Key point: Mitochondria make most of the cell's ATP
The mitochondria carry out cellular respiration, which uses oxygen to break down food molecules and store the energy as ATP. That is why they are called the "powerhouse" of the cell.
Wrong choices
- Ribosome: Ribosomes make proteins.
- Nucleus: The nucleus holds the cell's DNA.
- Golgi apparatus: The Golgi apparatus packages and ships proteins.
Question 2. Where in the cell are proteins assembled?
- ① Ribosomes
- ② Lysosomes
- ③ Mitochondria
- ④ Cell membrane
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Answer: ① Ribosomes
Key point: Ribosomes build proteins
Ribosomes read the instructions carried by messenger RNA (mRNA) and link amino acids together in the right order to build proteins.
Wrong choices
- Lysosomes: Lysosomes break down waste and worn-out cell parts.
- Mitochondria: Mitochondria make energy (ATP).
- Cell membrane: The cell membrane controls what enters and leaves the cell.
Question 3. In a DNA molecule, adenine (A) always pairs with which base?
- ① Uracil (U)
- ② Guanine (G)
- ③ Thymine (T)
- ④ Cytosine (C)
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Answer: ③ Thymine (T)
Key point: DNA base pairs: A–T and C–G
DNA bases pair in a fixed way: A with T and C with G. In RNA, uracil (U) takes the place of thymine, so A pairs with U.
Wrong choices
- Uracil (U): Uracil replaces thymine in RNA, not DNA.
- Guanine (G): Guanine pairs with cytosine.
- Cytosine (C): Cytosine pairs with guanine.
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