AP Biology :7.13 Origin of Life on Earth – Exam Style questions with Answer- FRQ

Question

Describe two pieces of biochemical and genetic evidence from extant and extinct organisms that support the hypothesis that all organisms on
Earth share a common origin of life.

▶️Answer/Explanation

Ans:

There are many pieces of biochemical and genetic evidence supporting
the hypothesis that all organisms on Earth share a common origin of life.
The following is an (incomplete) list:
• All organisms use the same genetic code to assemble polypeptides
from DNA nucleotide sequences.
• All organisms use the same enantiomer of amino acids (L-) and
sugars (D-).
• Gene sequence data shows successive, cumulative changes in gene
sequences in lineages (calibrated through time by the fossil record).
• All organisms share the same basic mechanisms of transcription,
translation, and DNA replication.
• Double-stranded DNA is the genetic information of all organisms.
• Prokaryotes and eukaryotes share similar cell structure.
• Eukaryotes share very similar cell structures.
• Organisms show remarkable similarity in their metabolic pathways
even though the possibilities within organic chemistry are almost
unlimited.
This is strong evidence that all life on Earth descended from a
common ancestor, thought to be a prokaryote. Almost all metabolic
pathways and all forms of nutrition evolved prior to the appearance of
eukaryotes (1 billion years ago). Glycolysis is common to every organism
and almost every cell. It evolved before the appearance of oxygen in the
atmosphere.

Question

According to the fossil record, prokaryotic cells were present on Earth for approximately 2.5 billion years before the first multicellular
organisms appeared.

Explain why it may have taken so long for multicellular life to appear on Earth.

▶️Answer/Explanation

Ans:

Multicellular organisms must have the ability to differentially
regulate gene expression in genetically identical cells to create tissues and
organs during development. From development throughout life,
multicellular organisms require a complex system of coordination and
communication. These processes require several different kinds of
molecules that can be detected and responded to in predictable ways. Cells
must also adhere to one another. They must be able to monitor the body and
coordinate over time and space.

Question

Describe two structural features of the neuron that support its function in the body and explain how each structural feature supports the specific function of that structure in the cell.

▶️Answer/Explanation

Ans:

The general function of a neuron is rapid communication between
cells, sometimes over very long distances. An individual neuron may
process information from many sources.

Question

Cellular respiration includes the metabolic pathways of glycolysis, the Krebs cycle, and the electron transport chain, as represented in the figures. In cellular respiration, carbohydrates and other metabolites are oxidized, and the resulting energy-transfer reactions support the synthesis of ATP.
(a) Using the information above, describe ONE contribution of each of the following in ATP synthesis.

  • Catabolism of glucose in glycolysis and pyruvate oxidation
  • Oxidation of intermediates in the Krebs cycle
  • Formation of a proton gradient by the electron transport chain

(b) Use each of the following observations to justify the claim that glycolysis first occurred in a common ancestor of all living organisms.

  • Nearly all existing organisms perform glycolysis.
  • Glycolysis occurs under anaerobic conditions.
  • Glycolysis occurs only in the cytosol.

(c) A researcher estimates that, in a certain organism, the complete metabolism of glucose produces 30 molecules of ATP for each molecule of glucose. The energy released from the total oxidation of glucose under standard conditions is 686 kcal/mol. The energy released from the hydrolysis of ATP to ADP and inorganic phosphate under standard conditions is 7.3 kcal/mol. Calculate the amount of energy available from the hydrolysis of 30 moles of ATP. Calculate the efficiency of total ATP production from 1 mole of glucose in the organism. Describe what happens to the excess energy that is released from the metabolism of glucose.
(d) The enzymes of the Krebs cycle function in the cytosol of bacteria, but among eukaryotes the enzymes function mostly in the mitochondria. Pose a scientific question that connects the subcellular location of the enzymes in the Krebs cycle to the evolution of eukaryotes.

▶️Answer/Explanation

Ans:

(a) The catabolism of glucose provides the raw materials for the further stages of cellular respiration. First, NADH is produced for use as a proton donor in the electron transport chain. Second, oxidized pyruvate is provided for the Krebs’s Cycle. The Krebs’s cycle produces NADH and FADH, which are   necessary proton donors in the electron transport chain, The formation of a proton gradient in the electron transport chain uses energy from the previous processes to pump protons across the inner membrane. This is necessary because the cell then harnesses the energy of this concentrations gradient by using the H+ ions to pass through the ATP Synthesis molecules which creates ATP by pressing ADP and Pi together.

(b) The fact that all organisms perform glycolysis is an example of a homologous cellular process and suggests all life are descended from one common ancestor capable of performing the reaction. Glycolysis occurring in anaerobic conditions is further evidence since the   early Earth atmosphere had low concentrations of O2 so the process had to be anaerobic. Finally, occurring in the cytoplasm is necessary because the process had to be performed by a very simple organism lacking internal membrane structures.

(c) Energy from hydrolysis of 30 md ATP = 30 mol . 73 kcal/mol  = 219 kcal

   1 md glucose . 30 mol ATP / mol glucose = 30 mod ATP  = 219 kcal

% Efficiency = 219 kcal / 686 kcal   100% = 31.9%

Excess energy is lost to the environment as heat.

(d) Do mitochondria I modern eukaryotes descend from endocytosed prokaryotes that could perform the kreb’s cycle?

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