Grade 8 Chapter 2 Study Review

Key Vocabulary

Flagellum: A whip-like structure that allows a cell to move.
Phytoplankton: Microscopic organisms that live in watery environments and perform photosynthesis.
Cilia: Hair-like structures on the surface of some cells that aid in movement and feeding.
Unicellular Decomposers: Organisms that consist of a single cell and break down dead organic material.
Hydra: A simple multicellular organism often studied in biology; it can regenerate and has a body with specialized cells.
Pseudopod: A temporary extension of a cell used for movement and feeding, typically seen in amoebas.
Diatom: A type of algae with a silica cell wall, important as primary producers in aquatic ecosystems.
Micro-sized: Referring to organisms or cells that are typically not visible to the naked eye.
Cell Division: The process by which a cell divides into two or more cells.
Cellular Respiration: A metabolic process where cells convert glucose and oxygen into energy, carbon dioxide, and water.
Microorganism: A microscopic organism, including bacteria, viruses, and fungi.
Multicellular: Organisms composed of multiple cells.
Specialized Cells: Cells that have specific roles and functions within an organism.
Unicellular: An organism that consists of a single cell.

Understanding Unicellular Organisms

Definition and Examples

A unicellular organism is defined as any living entity that consists of a single cell. Examples include bacteria, yeasts, and amoebas. These organisms are considered living things because they fulfill all criteria for life, including growth, reproduction, and response to stimuli.

Movement of Unicellular Organisms

Unicellular organisms move in various ways. For example, amoebas use pseudopods to extend their cell membrane and propel themselves in an environment, while flagellates have flagella that enable swimming.

Pseudopods and Amoebas

Amoeba Characteristics

Amoebas are typically found in moist environments such as ponds or soil. They lack a fixed shape and can change their form through the extension and retraction of pseudopods. Compared to animal cells, amoebas can engulf food particles through a process called phagocytosis, which is different from how multicellular organisms digest food.

Multicellular Organisms

Definition and Components

The term multicellular refers to organisms that comprise multiple cells working together to perform functions necessary for life. Examples include plants, animals, and fungi.

Specialized Cells

Specialized cells are tailored to perform specific tasks within an organism. For instance, red blood cells transport oxygen, while nerve cells transmit signals. Each type of specialized cell performs unique functions that contribute to the organism’s survival.

Acetabularia

Characteristics

Acetabularia, commonly known as mermaid’s wineglass, is a large unicellular organism belonging to the genus of green algae. It is an example of a unicellular organism due to its single cell structure while possessing specialized functionalities.

Cellular Processes in Unicellular Organisms

Diffusion and Osmosis

In unicellular organisms, processes such as diffusion and osmosis are crucial for maintaining homeostasis. Diffusion moves particles from areas of high concentration to low concentration, while osmosis specifically refers to the movement of water across a semipermeable membrane.

The Need for Specialized Cells in Multicellular Organisms

Multicellular organisms require specialized cells to efficiently perform various functions that a single cell cannot manage alone. These specialized cells collaborate, allowing the organism to grow, develop, and adapt to its environment.

Examples of Specialized Cells

Examples include muscle cells that perform contraction for movement and epithelial cells that form barriers to protect organs.

Hydra and Cellular Activities

Hydra Overview

A hydra is a simple multicellular organism that exhibits remarkable regenerative abilities. Its cells can perform various activities such as movement through muscle contraction and feeding by utilizing its tentacles.

Organelles and Their Functions

Energy Production

The organelle primarily responsible for breaking down carbohydrates to release energy is the mitochondrion. Specialized cells, like muscle cells, contain a high number of mitochondria to meet their energy demands.

Photosynthesis

Chloroplasts are critical for photosynthesis in plant cells. They contain chlorophyll, which captures sunlight and converts it into chemical energy.

Cellular Transport and Protein Production

When water, gases, and nutrients enter a cell, they diffuse through the cell membrane, affecting cellular activities. The organelle primarily responsible for protein synthesis is the ribosome, while the Golgi apparatus processes and packages proteins for export or use within the cell.

Function of Lysosomes

Lysosomes are organelles that contain enzymes to digest waste materials and cellular debris, playing a key role in cellular waste management.

Life Span of Cells

The lifespan of different cells varies considerably. For example, red blood cells live approximately 120 days, while skin cells may only last a few weeks. On average, billions of cells die each day in the human body due to various factors such as damage, apoptosis (programmed cell death), and normal wear and tear.

Cell Division

Process and Differences

Cell division is an essential process for growth and repair in multicellular organisms. It involves the replication of DNA and the distribution of organelles into daughter cells. In animal cells, the process differs from plants, primarily at the cell membrane and cell wall formation, which occur during cytokinesis.

Conclusion

This review of chapter 2 covers critical concepts surrounding unicellular and multicellular organisms, including their structures, functions, and the various processes that sustain them. Understanding these fundamental building blocks of biology lays the groundwork for more complex topics in cellular biology.

Grade 8 Biology - Chapter 2 Study Review

Grade 8 Biology - Chapter 2 Study Review