Problem 15 - Biology: Concepts and Applications

Question

Arrange these events in order of occurence, with 1 being the earliest and 6 the most recent. a. emergence of the noncyclic pathway of photosynthesis b. origin of mitochondria c. origin of protocells d. emergence of the cyclic pathway of photosynthesis e. origin of chloroplasts f. the big bang 1 ____ 2 ____ 3 ____ 4 ____ 5 ____ 6 ____

Step-by-Step Solution

Answer

1. f, 2. c, 3. d, 4. b, 5. e, 6. a.

Step 1: Identify the Earliest Event

The earliest event that would have occurred is the Big Bang, which is considered the birth of the universe itself. This event set the stage for all subsequent cosmic and biological developments.

Step 2: Determine the Origin of Life

The origin of protocells marks one of the earliest stages in the formation of life on Earth. Protocells are simple, pre-cellular structures that could perform basic life functions, and they likely evolved not long after Earth formed.

Step 3: Establish the Emergence of Photosynthesis

Next, we consider the emergence of photosynthesis. The cyclic pathway of photosynthesis, which does not produce oxygen, likely evolved first as a simpler form of photosynthesis found in ancient bacteria.

Step 4: Identify the Evolution of Mitochondria

The origin of mitochondria happened when a cell engulfed aerobic bacteria, leading to a symbiotic relationship. This event helped in the evolution of more complex organisms and was crucial for the development of eukaryotic cells.

Step 5: Determine the Origin of Chloroplasts

Following the evolution of mitochondria, chloroplasts arose in a similar way by engulfing photosynthetic bacteria. This allowed cells to perform photosynthesis efficiently and marked the origin of plant cells.

Step 6: Acknowledge the Development of Advanced Photosynthesis

Finally, the noncyclic pathway of photosynthesis evolved. This is a more sophisticated process that produces oxygen, and it played a significant role in transforming Earth's atmosphere and environment.

Key Concepts

The Big Bang

The Big Bang is widely accepted as the birth of the universe. This monumental event occurred approximately 13.8 billion years ago. Before the Big Bang, all matter and energy were concentrated in an extremely hot and dense singularity. Suddenly, this singularity expanded and cooled, leading to the formation of subatomic particles and simple atoms. Over billions of years, these particles combined to form stars, galaxies, and eventually planets. The Big Bang set the stage for everything that we see today. It marked the beginning of space, time, and all physical laws. Understanding this concept is essential to grasp the scale of time and space involved in the universe's history.

Photosynthesis Pathways

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy. It is fundamental to life on Earth, as it provides the primary energy source for nearly all ecosystems.

• Cyclic Pathway: This is believed to be the older form of photosynthesis. In cyclic photosynthesis, electrons are cycled back to the photosystem that originated them. This process does not produce oxygen and is found in some bacteria.
• Noncyclic Pathway: This is a more advanced form of photosynthesis that emerged later. It involves two photosystems and leads to the splitting of water molecules. As a result, oxygen is released as a by-product. This pathway is fundamental in producing the Earth's oxygen-rich atmosphere.

Both pathways are crucial for understanding how life evolved and adapted on Earth, significantly impacting the planet's composition and atmosphere.

Origin of Mitochondria

The origin of mitochondria is a key event in the evolution of life, instrumental in the development of eukaryotic cells. This organelle is the powerhouse of the cell, responsible for producing the energy currency of the cell, ATP, through a process called cellular respiration. The widely accepted theory for the origin of mitochondria is the endosymbiotic theory. This theory suggests that a primitive eukaryotic cell engulfed a free-living aerobic bacterium. Instead of digesting it, the cell formed a symbiotic relationship with the bacterium, which then became the mitochondrion. Over time, this relationship became permanent, with the mitochondrion providing the host cell with energy while receiving protection and nutrients. This event was critical as it enabled cells to efficiently utilize oxygen to produce energy, setting the stage for the evolution of complex multicellular organisms.

Origin of Chloroplasts

Chloroplasts are essential structures found in the cells of plants and some algae. They facilitate the process of photosynthesis, capturing light energy and converting it into chemical energy stored in sugars. The origin of chloroplasts, like mitochondria, is explained by the endosymbiotic theory. A symbiotic event similar to that of mitochondria occurred, where an early eukaryotic cell engulfed a photosynthetic cyanobacterium. Instead of being digested, the cyanobacterium was retained as a symbiotic partner, eventually evolving into the chloroplast. This relationship enabled the host cells to perform photosynthesis more efficiently.
The incorporation of chloroplasts marked a significant evolutionary step, giving rise to the vast diversity of plant life we see today. Their emergence was pivotal for sustaining life on Earth by contributing to oxygenating the atmosphere and providing food energy through the ecosystems.