ACT Prep Science College Board

Cell Biology

###Cell Structure and Function

• All living things are composed of cells; these are the smallest units considered fully alive and are often called the building blocks of life.
• A cell membrane surrounds abd protects the cell, controls what substances enter and exit the cell, and maintains the cell's environment.
• The nucleus is the control centre of the cell, containing the cell's genetic material (DNA).
• Cytoplasm is a jelly-like substance where most cellular processes occur, including metabolism and cell division.
• Mitochondria are the powerhouses of the cell, where respiration happens to supply energy for the cell.
• Ribosomes are sites for protein synthesis, providing essential proteins for the cell's functions.

###Cell Division

• The process of cell division is essential for growth, repair, and reproduction in organisms.
• The stages of cell division include interphase, prophase, metaphase, anaphase, and telophase; these make up the cell cycle.
• Mitosis is a type of cell division that results in two identical daughter cells, each having the same number of chromosomes as the parent nucleus.
• Meiosis is a type of cell division that produces four haploid cells, which have half the number of chromosomes; this is crucial for sexual reproduction.

###DNA and Genetic Information

• DNA (Deoxyribonucleic acid) is the molecule that carries genetic information.
• DNA has a double helix structure held together by bonds between base pairs - Adenine (A) bonding with Thymine (T), and Cytosine (C) bonding with Guanine (G).
• The sequence of these bases determines an organism's traits, forming genes which are coded instructions for making proteins.

###Cellular Respiration

• Cellular respiration is the process by which cells convert nutrients into energy.
• This occurs mainly in mitochondria and includes the stages of glycolysis, the Krebs cycle, and the electron transport chain.
• The equation for respiration is: glucose + oxygen -> carbon dioxide + water + energy.

###Properties of Life

• All cells display certain properties, including growth, response to stimuli, reproduction, and the release of waste products.
• Homeostasis is the maintenance of a stable internal environment in response to changes in external conditions, enabling cells (and therefore, organisms) to function efficiently.

###Active and Passive Transport

• Cells interact with their environment by various methods including passive transport (diffusion and osmosis) and active transport (requires energy to move substances against a concentration gradient).
• Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a selectively permeable membrane.
• Diffusion is the passive movement of particles from an area of high concentration to an area of lower concentration.
• Active transport requires energy in the form of ATP to move substances against their concentration gradients.