Cell Biology: Growth and Reproduction

Cell Growth, Division & Reproduction

• Single-celled organisms are very small and often invisible to the naked eye. Larger organisms are made of numerous tiny cells, not a few large ones.
• Some organisms reproduce asexually and some sexually.
• Cells in a human body reproduce asexually continuously, while the human organism itself reproduces sexually.

Surface Area to Volume Ratio

• A cell's size creates a surface area-to-volume ratio problem. As a cell gets larger, its volume increases faster than its surface area.
• To find a cube's surface area, calculate the area of one side and multiply by six. Surface area is length times width for each side.
• To find a cube's volume, multiply length times width times height.
• Volume increases faster than surface area in growing cells.

Cell Growth Limitations

• Cell growth requires more materials to move across the cell membrane.

• Increasing volume of a cell means there are not enough "traffic lanes" (surface area) for materials to move across the membrane.

• Materials like nutrients and oxygen need to enter efficiently into the cell and waste products leave with equal efficiency. Too much volume relative to surface area causes the exchange process to slow to a crawl.

• If a cell gets too large, not enough material can pass through its membrane fast enough to sustain the cell, hindering growth.

Cell Division

• To solve the surface-area-to-volume ratio problem that growing cells face, cells divide, producing two "daughter cells".
• Sufficient DNA must be present to ensure each daughter cell has enough to support its own function. Before cell division, DNA must replicate, thereby creating a backup for the daughter cells.

Asexual Reproduction

• Reproduction is important for life. For single-celled organisms like bacteria, simple cell division creates a simple form of reproduction.
• Asexual reproduction is a fast method of creating many genetically identical "offspring"
• This form of reproduction is known as binary fission, and is a rapid method for population growth and survival.

Sexual Reproduction

• Multicellular organisms like humans reproduce through sexual reproduction.
• Sexual reproduction creates offspring that are not genetically identical to either parent.
• Sexual reproduction involves the fusion, or combination, of cells like egg and sperm.

Comparing Sexual and Asexual Reproduction

• Asexual reproduction is fast when resources needed for survival are abundant
• When environmental conditions are stable, and offspring must be genetically identical to their parent, asexual reproduction is the preferred method.
• Sexual reproduction generates offspring that are not genetically identical to either parent. This allows for more genetic variation, which is essential when environments are changing and new combinations of traits are beneficial.

Explore the fundamental concepts of cell growth, division, and reproduction in this quiz. Understand how single-celled and multi-celled organisms differ in their reproductive strategies and the implications of surface area to volume ratios in cells. Discover the limitations faced by cells as they grow and how these factors influence their functionality.