Biology Cells

Study Notes

Cells are the structural units of all living things
Most cells are composed of four elements: carbon, hydrogen, oxygen, and nitrogen
Cells are approximately 60% water

A cell has three main regions or parts: nucleus, cytoplasm, and plasma membrane
The nucleus is the first layer, cytoplasm is the middle layer, and the plasma membrane is the outer layer

Surface extensions found in some cells: cilia, flagella, and microvilli
Cilia move materials across the cell surface, located in the respiratory system to move mucus
Flagella propel the cell, with the only flagellated cell in the human body being sperm
Microvilli are tiny, finger-like extensions of the plasma membrane that increase surface area for absorption

Fibroblast cells connect body parts and secrete cable-like fibers
Erythrocyte (red blood cell) carries oxygen in the bloodstream and connects body parts via blood vessels
Epithelial cells cover and line body organs, packing together in sheets with intermediate fibers that resist tearing during rubbing or pulling
Skeletal muscle and smooth muscle cells move organs and body parts, with contractile filaments that allow cells to shorten forcefully
Fat cells store nutrients, with lipid droplets stored in the cytoplasm
White blood cells, such as the macrophage, fight disease by digesting infectious microorganisms
Nerve cells (neurons) gather information and control body functions, receiving and transmitting messages to other body structures
Oocyte (female) and sperm (male) cells are responsible for reproduction, with the oocyte being the largest cell in the body

Passive transport requires no energy and includes diffusion, osmosis, filtration, and facilitated diffusion
Active transport requires energy and includes transport by pumps and vesicles
Passive processes: diffusion and filtration
Diffusion is the movement of molecules from high concentration to low concentration, down a concentration gradient
Osmosis is the movement of water molecules
Facilitated diffusion is the movement of lipid-insoluble molecules, such as glucose
Hypertonic solutions contain more solutes than the cells, causing cells to shrink
Hypotonic solutions contain fewer solutes than the cells, causing cells to swell
Active processes use ATP to move substances across a membrane
Sodium-potassium pump is an example of active transport
Vesicular transport includes exocytosis, endocytosis, phagocytosis, and pinocytosis

The skin is composed of two main layers: epidermis and dermis
The epidermis has two sublayers: stratum basale and stratum corneum
The stratum basale is the deepest layer of the epidermis, where daughter cells are pushed upward to become the more superficial layers
The stratum corneum is the outermost layer of the epidermis, composed of shingle-like dead cells filled with keratin
The dermis has two sublayers: papillary layer and reticular layer
The papillary layer contains dermal papillae, which indent the epidermis above and increase friction and gripping ability on palm and sole surfaces