The Cell (Cytology)

Introduction to Botany

What is cell theory?

The cell is the fundamental unit of life and smallest unit - with no cells there would be no life

Properties of cells

• take in raw materials

• extract energy

• synthesize molecules

• exhibit organized growth (except tumor cells or galls in plants)

• respond to stimuli

• reproduction

• plant cells are small

Cell structure

Prokaryotic: “before nucleus” - no nucleus, bacteria, cyanobacteria = genetic material not enclosed in nucleus because it doesn’t have one

Eukaryotic: true nucleus, cells of all other organisms (except viruses)

Plant’s cell wall

plasma membrane, rigid cell walls, middle lamella, plasmodesmata

Plant’s cell internal elements

cytoplasm, nucleus (stores DNA and has cell activity), large vacuole (food, water, metabolic waste), chloroplasts, mitochondria (the power plant), ribosomes (protein synthesis), dictyosomes/Golgi bodies (modification of transport of proteins), endoplasmic reticulum (transport of cellular materials)

Plant cell walls

(not in animals)

• They support, enclose, and protect

• They are made out of microfibrils of cellulose - the layers form a lattice (criss-cross = more sound structure), porous but rigid

Primary cell wall

(in all plants)

• Contains cellulose and pectins (plus polysaccharides and sometimes lignins)

• Just outside cell membrane

Secondary cell wall

• Inside of the primary cell wall

• Not in all plant cells

• Made of cellulose and lignins = strength/hardness and in woody plants

Middle lamella

• Consists mainly of pectin

• Between cells = “cement” that binds cells together

Plasmodesmata (channel)

• Direct cytoplasmic (fluid) connections between cells

• Passage of materials between cells

• Communication and coordination

Protoplasm

Living portion of the cell

• inside the cell wall

• bounded by plasma membrane

Plasma membrane

Phospholipid bilayer surrounding the cytoplasm

• selective barrier = regulates movement of materials

• proteins embedded in or on surfaces (fatty acids pointed towards each other) - some work as enzymes

Cytoplasm

Fluid interior of cell

• chemical reactions

• contains organelles - small, often with membrane, often submicroscopic, specific functions

Nucleus

• Separate from cytoplasm

• Large

• contains chromatin

• contains genetic material

• chromosomes - specific in number, visible during cell division

• contains DNA - directs chemical activities of call