Biology Chapter: Characteristics of Life

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Questions and Answers

Which of the following is NOT a characteristic of life?

Does not require energy (correct)

Composed of cells

Can evolve

Can reproduce

What is the basic unit of life?

Organ

Organism

Tissue

Cell (correct)

Which of the following is NOT a reason viruses are considered non-living?

They are incredibly small (correct)

They contain nucleic acids

They rely on living cells for reproduction

They lack a metabolism

What is the process by which living organisms maintain a stable internal environment?

Homeostasis (C) Signup and view all the answers

What is the term for the ability of living organisms to sense and respond to changes in their environment?

Irritability (A) Signup and view all the answers

What is the approximate age of the Earth?

4.6 billion years (D) Signup and view all the answers

What is the earliest evidence of life on Earth?

Fossil evidence of prokaryotic cells (B) Signup and view all the answers

What crucial factor allowed life to originate on Earth?

The existence of liquid water (A) Signup and view all the answers

Which of the following is NOT a major macromolecule essential for life?

Minerals (D) Signup and view all the answers

What is the key characteristic that distinguishes eukaryotes from prokaryotes?

The presence of a nucleus (D) Signup and view all the answers

What is the significance of clay in the formation of life?

Clay provides a surface for the polymerization of amino acids. (B) Signup and view all the answers

What is the primary function of lipid spheres (liposomes) in the origin of life?

To provide a protective barrier around early cells. (C) Signup and view all the answers

Which of the following is a characteristic of probionts?

They are enclosed by a membrane. (A) Signup and view all the answers

What is the role of RNA in the central dogma of life?

RNA acts as a messenger, carrying genetic information from DNA to ribosomes. (D) Signup and view all the answers

How does the central dogma differ in early life compared to modern life?

RNA was the primary form of genetic information in early life, rather than DNA. (D) Signup and view all the answers

Which of the following is NOT a molecule found in the primordial atmosphere?

Oxygen (O2) (C) Signup and view all the answers

Why were the molecules in the primordial atmosphere so reactive?

They contained an abundance of electrons. (D) Signup and view all the answers

What was the primary source of energy for the formation of biological molecules in the Miller-Urey experiment?

Sparkling electrodes. (A) Signup and view all the answers

What kind of molecules were produced in the Miller-Urey experiment?

Simple organic molecules like amino acids and urea. (C) Signup and view all the answers

Which of the following molecules, when added to the Miller-Urey experiment, led to the formation of purines and pyrimidines?

Hydrogen cyanide (HCN) and formaldehyde. (B) Signup and view all the answers

What is the role of deep-sea vents in the origin of life hypotheses?

They provide heat and reduced molecules needed for life's beginnings. (C) Signup and view all the answers

What is the significance of carbonaceous chondrite meteorites in the extraterrestrial origin of life hypothesis?

They contain a variety of organic molecules, including amino acids and purines. (C) Signup and view all the answers

What is required for monomers to form polymers, such as proteins and DNA?

A source of energy and specific conditions. (B) Signup and view all the answers

What is the primary function of ribozymes?

To catalyze biological reactions (B) Signup and view all the answers

What is the main reason DNA replaced RNA as the primary carrier of genetic information?

DNA is more stable than RNA. (A) Signup and view all the answers

Which of the following is NOT a prokaryotic characteristic of mitochondria and chloroplasts?

Presence of a nucleus (B) Signup and view all the answers

What advantage did proteins offer over RNA in terms of biological catalysis?

Proteins have a wider range of potential structures. (A) Signup and view all the answers

What is the primary mechanism through which some genes from the proto-endosymbiont were transferred to the nucleus of the host cell?

Horizontal gene transfer (C) Signup and view all the answers

What is the significance of ATP in the context of early life?

ATP provided energy for the synthesis of proteins. (A) Signup and view all the answers

How did the emergence of oxygenic photosynthesis significantly impact the early Earth?

It created an atmosphere rich in oxygen, paving the way for more complex life. (D) Signup and view all the answers

What is one advantage that eukaryotes gain from the presence of specialized mitochondria?

Greater energy production (C) Signup and view all the answers

Which type of prokaryotic cell is believed to be the ancestor of chloroplasts?

Cyanobacteria (A) Signup and view all the answers

What is the defining characteristic of eukaryotes that sets them apart from prokaryotes?

The presence of a nucleus. (A) Signup and view all the answers

Which of the following is NOT a characteristic of early eukaryotic cells?

Presence of linear DNA molecules. (A) Signup and view all the answers

Why is RNA considered the primary genetic material in the earliest life forms?

RNA can act as both genetic material and catalyst (A) Signup and view all the answers

Which of the following organelles is believed to have originated from an ancient symbiotic relationship with a bacterium?

Mitochondria (B) Signup and view all the answers

Study Notes

Defining Life and the Chemistry of Life

Life is defined by characteristics, including eating, surviving, and reproducing.
Life is composed of cells.
Key characteristics shared by all living things include a hierarchy, harnessing and utilizing energy (metabolism), sensing and responding to stimuli, regulating through homeostasis, and having genetic material that allows for growth, reproduction, and independent evolution.
Viruses do not meet all the requirements of life, containing nucleic acids but lacking cellular machinery and metabolism, relying on living cells for reproduction.

Overview

The study of life covers what life is, its chemical origins, the macromolecules of life, the earliest forms of life, eukaryotic cells, and multicellularity.

Properties of Life

Life is composed of cells.
Living organisms display a hierarchical organization and utilize energy (metabolism), sensing and responding to stimuli.
They regulate through homeostasis and have genetic material to grow, reproduce, and evolve.

How Life Originated

Earth formed 4.6 billion years ago.
Life likely started around 3.8-4 billion years ago.
The first clear fossil evidence of prokaryotic cells occurred 3.6 billion years ago.
This involved the formation of biomolecules, their assembly into cell-like structures, and the acquisition of genetic capability by one or more biomolecules.
Earth's habitable zone allows for liquid water and is crucial for life as we know it.

Origins of Life - Prokaryotes

Early Earth had no cells, hence no life.
At one point, there were no cells and thus no life. Prokaryotes, including bacteria and archaea emerged later.

Origins of Life - Eukaryotes

Eukaryotes emerged about 2 billion years ago.
Animals emerged 525 million years ago.
Humans have existed for roughly 150,000 years.

Evolution of Life

Evolution of life involved several key steps, including the formation of biomolecules, assembly into cell-like structures, and acquisition of genetic capabilities by one or more biomolecules.

Biologically Important Molecules

Life is built on major macromolecules (biomolecules): nucleic acids, proteins, lipids, and carbohydrates.
These can develop from simpler molecules.

How Did Biomolecules Originate?

There are three main hypotheses for biomolecule origin: a reducing atmosphere, deep-sea vents, and extraterrestrial origins.

Reducing Atmosphere

The primordial atmosphere (4 billion years ago) likely contained water vapor (H₂O), hydrogen (H₂), ammonia (NH₃), methane (CH₄), and no oxygen (O₂).
Early molecules (H₂, CH₄, NH₃) have a high abundance of electrons.
This atmosphere contained reactive molecules that facilitated the formation of more complex molecules.

UV Light and Lightning

The lack of ozone in the early atmosphere allowed energetic UV light to reach the lower atmosphere.
Lightning was also a common energy source.

Miller-Urey Experiment

Stanley Miller (1953) simulated the early Earth's reducing atmosphere.
He mixed gases (H₂, CH₄, NH₃, H₂O) in a closed chamber and sparked electrodes to provide energy.
After a week, many organic molecules, including urea, amino acids (e.g., lactic acid, formic acid, acetic acid) were detected.
These molecules are key components of living organisms.

More Complex Molecules

When hydrogen cyanide (HCN) and formaldehyde were added to the Miller-Urey experiment, more complex molecules (such as purines, pyrimidines, components of nucleic acids) and other biomolecules were formed.
Sugars like glyceraldehyde, ribose, glucose, and fructose were also detected.

Role of Deep Sea Vents

Deep-sea vents also provided heat and reduced molecules (methane, ammonia, hydrogen sulfide) for the formation of biomolecules.

Extraterrestrial Origins

Organic molecules may have come from space via carbonaceous chondrite meteorites.
These meteorites are rich in organic molecules, including amino acids (glycine, glutamic acid, alanine) and purines and pyrimidines.

From Monomers to Polymers

Polymers (macromolecules like proteins, DNA) form when monomers (simple molecules like amino acids) bond together.
Solid surfaces (like clays) could have provided a friendly environment ("clay hypothesis") for polymerization.

Key Attribute of Life

Life requires defining compartments (membranes) to separate reactions.
It requires genetic information storage and translation into proteins.
Pathways are needed to obtain and use energy.

Lipid Spheres (Liposomes)

Lipid spheres (liposomes) are compartments that separate reactions within a space, a key step in early cell development.
Probionts, or abiotically produced organic molecules, are surrounded by a membrane.

Probionts

Probionts can spontaneously form bilayer structures, similar to lipid vesicles.
These are selectively permeable, meaning only certain molecules can pass through.
Clays can accelerate the formation of lipid vesicles.

The Central Dogma

In modern life, DNA is copied into RNA, which then guides protein synthesis.
Proteins carry out life's functions.

RNA World

RNA may have initially been both the genetic material and the catalyst (ribozymes) responsible for life's functions.
RNA molecules fold into specific shapes to perform these functions, including carrying information.

RNA Replaced by DNA & Proteins

Specialized molecules emerged for stable information storage (DNA) and catalytic functions (proteins).
Some RNA molecules may be able to direct small protein synthesis; proteins provide much more variability.
DNA is chemically more stable than RNA.

Simple Oxidation Reduction Reactions

Early reactions were simple steps, eventually evolving into more complex, efficient multistep ones.
Adenosine triphosphate (ATP) acts as an energy carrier, combining energy-releasing and energy-requiring reactions.

Earliest Forms of Life

Stromatolites are the earliest fossilized evidence of life.
They are formed by photosynthetic bacteria (cyanobacteria).
Oxygenic photosynthesis is crucial, using sunlight to oxidize water.

Common Ancestor

Present-day organisms are categorized into three domains: Archaea, Bacteria, and Eukaryotes.
They all share a common ancestor (LUCA—last universal common ancestor).

Eukaryotic Cells and Multicellularity

Eukaryotes arose approximately 2.5 billion years ago.
Key characteristics of eukaryotes include:
- Separation of DNA and cytoplasm via a nuclear envelope.
- Membrane-bound compartments, or organelles, with specialized functions.
Other organelles include mitochondria, chloroplasts, endoplasmic reticulum, and Golgi complex.

Endosymbiotic Theory

Chloroplasts and mitochondria evolved from free-living prokaryotic cells.
Mitochondria originated from aerobic bacteria.
Chloroplasts originated from photosynthetic cyanobacteria.
These cells were engulfed by larger prokaryotic cells, forming an endosymbiotic relationship.

Endosymbiosis and Horizontal Gene Transfer

Some proto-endosymbiotic genes became redundant and were lost.
Other genes were relocated to the nucleus.
Horizontal gene transfer also occurred.

Why Eukaryotes?

Specialized mitochondria support greater energy production.
Larger genomes and more complex cells are allowed.
Evolution of specialization and multicellularity is enhanced.

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Explore the fundamental characteristics that define life through this engaging quiz. Learn about the basic units of life, the origins of life on Earth, and the role of macromolecules and RNA. Test your knowledge and understand the distinctions between living organisms and viruses.