End of Year 2025

Question 1

List and describe the nine major animal phyla.

Answer 1

1. Porifera (sponges)—The sponges lack true tissue.
2. cnidaria—The cnidarians have true tissues and radial body symmetry.
3. Platyhelminthes— The flatworms are protostomes and acoelomates, bilaterians.
4. mollusca—They are protostomes, and bilaterians.
5. Annelida— The segmented worms are triploblastic coelomates.
6. Nematoda—The roundworms are protostomes and bilaterians.
7. Arthropoda— The arthropods are ecdysozoans. They possess segmented appendages. They are protostomes and bilaterians.
8. Echinodermata—The echinoderms are deuterostomes. They are bilaterians and have skin covered with spines for self-defense.
9. Chordata—Chordates are deuterostomes and bilaterians that possess a post-anal tail.

Question 2

List and describe the eight stages in meiosis and show how they compare to the stages in mitosis.

Answer 2

Prophase 1 - The chromosomes condense, and the nuclear envelope breaks down. Crossover occurs.
Metaphase 1 - homologous chromosome pairs (tetrads) line up along the equator of the cell
Anaphase I - involves homologous chromosomes being pulled apart towards the equator of the cell.
Telophase & Cytokinesis 1: The chromosomes arrive at opposite poles, and the nuclear envelope reforms around each set, dividing the cell’s cytoplasm and resulting in two daughter cells, each with a haploid number of chromosomes.

Prophase 2 - a new spindle forms around the chromosomes
Metaphase 2 - chromosomes line up at equator of cell.
Anaphase 2 - centromere’s divide chromatids move to the opposite poles of the cell
Telophase & Cytokinesis 2 - a new nuclear envelope forms around each set of chromosomes in the cytoplasm and divides.

Question 3

State the six modern tenets of the cell theory

Answer 3

(1) All living organisms are composed of cells.
(2) the cell is the basic unit of structure and function in living organisms
(3) Cells arise from pre-existing cells.
(4) Energy flow occurs within cells.
(5) Cells contain hereditary information passed to daughter cells during cell division.
(6) All cells have a similar chemical composition.

Question 4

Describe DNA replication, including the role of major enzymes.

Answer 4

Initiation: DNA replication begins at specific locations on the DNA molecule called origins of replication. Proteins bind to these sites, unwinding the double helix and separating the two strands of DNA.

Unwinding: The enzyme helicase plays a crucial role by unwinding the DNA strands, creating a replication fork where the two strands separate. Single-strand binding proteins stabilize the unwound DNA to prevent it from rejoining.

Priming: Before new DNA strands can be synthesized, a short RNA primer is needed. The enzyme primase synthesizes this RNA primer, which provides a starting point for DNA polymerase to begin adding nucleotides.

Elongation: DNA polymerase then adds nucleotides to the growing DNA strand by complementary base pairing (A with T and C with G). This process occurs continuously on one strand (leading strand) and in short segments on the other strand (lagging strand), forming Okazaki fragments.

Replacing RNA primers: Once the new DNA strands are formed, the RNA primers are removed and replaced with DNA nucleotides. The enzyme DNA polymerase I typically carries out this replacement.

Ligation: The final step involves sealing the gaps between the newly synthesized DNA fragments. The enzyme DNA ligase joins the Okazaki fragments on the lagging strand, creating a continuous DNA molecule.

At the end of DNA replication, two identical double helices are produced, each consisting of one original strand and one newly synthesized strand. This ensures that genetic information is accurately passed on to daughter cells during cell division.

Question 5

List and describe the four major classes of biomolecules

Answer 5

Carbohydrates: These are organic compounds of carbon, and oxygen. Carbohydrates are primarily energy sources for living organisms. Examples include glucose, sucrose, and starch.

Lipids: Lipids are a diverse group of hydrophobic (water-repelling) molecules, primarily composed of carbon and hydrogen. They serve essential roles, including energy storage, structural components of cell membranes, and signaling molecules. Common types of lipids include fats and oils, phospholipids, and steroids.

Nucleic Acids: These biomolecules are essential for storing and transmitting genetic information. Nucleic acids comprise nucleotide monomers, consisting of a sugar, a phosphate group, and a nitrogenous base. The two main types are DNA, which stores genetic information, and RNA, which plays various roles in protein synthesis and gene regulation.

Proteins: Proteins are made up of amino acids linked together by peptide bonds. They serve many functions, including acting as enzymes, hormones, structural components, and transport molecules. The specific sequence and structure of amino acids determine a protein’s function. There are 20 different amino acids, and their unique combinations and arrangements allow for an immense variety of proteins, each with a specific role in the cell.

Question 6

Cellular Respiration

Answer 6

• Glycolysis
  
  • Breaking of glucose releases ATP and NADH.🤌🏻
• Oxidation of Pyruvate
  
  • Pyruvate is turned into Acetyl CoA.😘
• Krebs Cycle
  
  • Turns Acetyl CoA into other six-carbon compounds
• Oxidative Phosphorylation
  
  • Electron Transport Chain (ETC) uses NADH, which charges ADP molecules into ATP for future use😱!

Question 7

Explain how muscle contraction occurs.