Question

The cell theory states that a. all living things are composed of cells. b. cells are the smallest units of living organisms. c. new cells come from pre-existing cells by cell division. d. all of the above. e. only a and b are true.

Short answer

The correct answer is D: all of the above.

Step-by-step solution

Understand the cell theory

The cell theory is a fundamental concept in biology, and it's composed of three key points: \n1) All living organisms are composed of one or more cells. \n2) The cell is the basic unit of structure and organization in organisms. \n3) Cells arise from pre-existing cells.

Analyze the given options

Look closely at each option and decide if it aligns with all three principles of the cell theory. \nA) aligns with the first principle of cell theory, \nB) aligns with the second principle, \nC) aligns with the third principle, \nE) includes only the first two principles, and \nD) suggests all the statements are part of the cell theory.

Pick the correct answer

The correct answer should include all three principles of cell theory. Looking at the options, only D encompasses all these principles. Therefore, D) all of the above, is correct.

Key concepts

Basic Unit of Life

The concept of the cell as the basic unit of life is central to understanding biology. Cells are the fundamental building blocks of all living organisms, from the tiniest bacteria to the largest whales. But what does it mean to be the 'basic unit of life'? Essentially, it implies that cells are the smallest entities that can carry out all the functions of life. This includes the ability to grow, respond to their environment, metabolize nutrients, and reproduce.

Every cell is enclosed by a membrane that protects it from the outside environment and controls the movement of substances in and out of the cell. Inside, cells are equipped with all the machinery necessary for life, such as ribosomes for making proteins and DNA which contains the genetic blueprint. Think of cells as self-contained packets of life that, although incredibly varied, all share these fundamental characteristics.

In the context of the exercise from the textbook, it is made clear that the statement 'cells are the smallest units of living organisms' aligns perfectly with the cell theory. This emphasizes that, regardless of the organism's complexity, the cell is the fundamental component of its structure and function.

Cellular Organization

Organization at the cellular level is a marvel of nature. Cellular organization refers to how cells are structured to perform life functions efficiently. In multicellular organisms, like humans, cells are not just randomly thrown together but organized into tissues, organs, and organ systems that work in harmony. Similarly, within a single cell, countless molecules and organelles are systematically arranged to facilitate life processes.

Each cell type has a specific role, with its structure adapted accordingly. For example, red blood cells are shaped and organized to maximize their oxygen-carrying capacity, while nerve cells have long extensions that aid in transmitting electrical signals over distances. This organized complexity allows cells to work together in a coordinated manner, which is pivotal for the organism's survival and function.

Considering cellular organization enhances our understanding of the statement in the exercise that all living things are composed of cells. It's not just about being made up of cells; it's how these cells are meticulously organized to form the complex beings we observe in the natural world.

Cell Division

Cell division is the process by which a parent cell divides into two or more daughter cells. It's a fundamental aspect of life, enabling organisms to grow, repair damaged structures, and reproduce. There are two main types of cell division: mitosis, which results in two identical daughter cells, and meiosis, which produces four genetically different cells for the purpose of sexual reproduction.

Mitosis is used for growth and maintenance in multicellular organisms and also for asexual reproduction in some single-celled organisms. During mitosis, a cell makes a copy of its DNA and divides its contents equally to form two new cells that are clones of the original. Meiosis, on the other hand, occurs in the sexual organs and is the process behind genetic diversity among offspring.

The third statement in the exercise embodies this concept, acknowledging that 'new cells come from pre-existing cells by cell division.' This is a cornerstone of life's continuity, ensuring that genetic information is passed down to future generations and making evolution and natural selection possible.