Plant Cells

What are Cells?

• ROBERT HOOKE– 1665 discovered tiny

compartments in cork which he called “cells”

History

• 1675- Malpighi, Italian physician, published an account of the microscopic, internal structure of plants

• 1838- Matthias Scheiden and Theodore Schwann, “Cell Theory”

• 1846- von Mohl, termed the viscous liquid which he found on boxlike cell plants and animal cell as protoplasm

Cell Theory

Bodies of all plants and animals are composed of structural unit called “Cell”

Cells

Are the basic structural and functional unit

All living organisms are made up of cells

Physiological processes are encountered and manifested at cellular level.

Prokaryote vs. Eukaryote

Prokaryote• Cells without nucleus and

other membrane bound organelles

• Chromosomes made up of DNA only

• Present in eubacteria and archaebacteria

Eukaryote• Cells with nucleus and

membrane bound organelles

• Chromosomes are made up of DNA and protein

• Present in fungi, protists, plants and animals

Prokaryote vs. Eukaryote

Prokaryote Eukaryote

Plant Cells

Cell Wall

• Encloses and protects the cell components• Plays a vital role in cell division and cell expansion• Composed of overlapping cellulose, microfibril,

other polysaccharide and varying amount of lignin• Plasmodesmata- function in communication

between cells- important in facilitating the flow of water and mineral between conducting cell

Cell Wall

• Middle lamella- region between the primary walls of adjacent cell

- Composed of cementing substance called “pectin”

• Other substance that may be present in the cell wall are gums, resin, silica, calcium carbonate, waxes and cutin and both structural protein and enzyme

Plasma Membrane

• Semi-permiable membrane encloses the cytoplasm within a cell

• Composed of variable amounts of fat type molecules (lipids) and protein

• Has within it channels for the movement of ions such as potassium (K+), calcium (Ca2+) and Hydrogen (H+)

Cytoplasm

• Is a liquid, gel like substance and contain several type of organelles

Vacuoles

• In a mature plant cell, one large vacuole occupies most of the space within the cell

• Surrounded by a single layered membrane• Functions in regulation of osmotic balance and

turgidity of the cell, and it stores secondary metabolite

Nucleus

– Enclosed by a double membrane that has pores in it to allow communication with the cytoplasm

– Within the nucleus are chromosome which contain DNA needed to create proteins within the cell

– Also present in the nucleus are one or more nucleoli containing RNA

– The rest of the nucleus is filled by nucleoplasm

Organelles

• Plastids- classified by the primary pigment the plant contains

a. Chloroplast- plastid where photosynthesis takes place- in higher plants it is usually oval-shaped and it is surrounded by a double membrane- within it are sac like structure called “thylakoid”

Organelles

- A stack of thylakoids is called granum, this is where green chlorophyll pigments are located- chlorophyll and proteins bound to the thylakoid use light energy to make simple sugar from carbon dioxide and water

b. Leukoplast- colorless plastid contain storage product which includes protein bodies or starch grain

Organelles

c. Chromoplast- Plastids that are red, orange, yellow

depending on the pigment they contain- As fruit color change, so do the plastid

structure, pigment type and content

Organelles

• Mitochondria - Surrounded by a double membrane- The inner of these two membrane has

infolding called “Cristae” , that protrude into the cavity within

- Primary site of enzyme controlling respiration

Organelles

• Ribosome- They contain ribosomal RNA and function in

protein synthesis- Also found in cytoplasm and associated with

Endoplasmic reticulum in the cytoplasm

Organelles

• Ribosomes- Contain ribosomal RNA and function in protein

synthesis- Also found in cytoplasm and associated with

endoplasmic reticulum in the cytoplasm

Organelles

• Dictyosome/ Golgi Bodies– These organelles appear appears as a flattened

sacs and associated vesicle– Produce and secrete cell wall polysaccharide

precursor and complex carbohydrate substance that are secreted out of root cap cell

Organelles

• Endoplasmic Reticulum– System of membranous tubules and sac– Primary function of the ER is to act as internal

transport system that allows molecules to move form one part of the cell to another

a. Smooth Endoplasmic Reticulum- Has no 80s ribosome

b. Rough Endoplasmic Reticulum- Site of Protein synthesis studded with 80s ribosome

Organelle

• Microbodiesa. Lysosomes- spherical or sac like

- capable of digesting unwanted molecules in the cell

under acidic condition - function in resorption and

phagocytosis

Organelles

b. Peroxisome - similar appearance to lysosome - contain a variety of enzymes - rid of toxic substances hydrogen peroxide (a

common by product of cellular metabolism)

Organelles

c. Glyoxysomes - another type of microbody - contain enzymes

Function: - convert stored fats into sugar

Plant Cells

Crystals

Composition • Calcium Oxalate (CaC2O4)

• Calcium Carbonate (CaCO3)

Types of Crystal• Raphides- Needle like • Rosette- star or rose like• Prismatic- Prism or diamond• Styloid- Knife like

• Cystolith- grape-like