Botany Cells and Cell Growth

plants have two systems

root system and shoot system

shoot system

aboveground, vegetative organs (leaves and stems)

-reproductive organs: flowers and fruits

root system

underground, one organ: roots

determinate growth

maximum size genetically determined

-growth stops over time, usually cannot heal/grow, max size rarely achieved in nature, leaves flowers fruits

indeterminate growth

no max size genetically

-able to keep growing through life

-usually can heal/grow

-limited by resources and environmental factors

-roots and stems

Cell theory

1665 - Robert Hooke sees 'chambers' on cork tissue under microscope - calls them "cells"

• 1838 - Schleidern and Swann stated that:

1. All plants and animals are made of cells

2. Cell is the basic unit of life

• 1858 - Virchow added that:

3. Cells arise by reproduction from previous cells - "Omnis cellula e cellula"

all cells contain same 4 components

cell membrane, cytoplasm, DNA, ribosomes

cell membrane

• A phospholipid bilayer with embedded proteins

• Serves as a barrier between the cell and the environment

• Controls the passage of organic molecules, ions, water, oxygen, and cellular waste (carbon dioxide and ammonia)

cytoplasm

Entire region of the cell between the plasma membrane and the nuclear envelope

• Comprised of organelles suspended in a gel-like material - the cytosol - and protein threads - the cytoskeleton

• Provides the structure for different components of the cell

DNA nucleus

• In eukaryotic cells, DNA is typically housed in the nucleus

• Directs the synthesis of ribosomes and proteins.

• Stores chromatin (DNA + proteins)and the nucleolus (where ribosomes are made)

.• Separated from the rest of the cell by the nuclear envelope (a double membrane)

plants more common for _____

polyploidy

DNA chromatin vs chromosomes

• During cellular replication, DNA is visible in the form of chromosomes (linear in eukaryotes)

• During cellular growth and maintenance, proteins attach to chromosomes, making them resemble jumbled threads - this is chromatin

ribosomes

Structures responsible for protein synthesis

• They are NOT organelles!

• Can either float free in the cytoplasm or be embedded in the endoplasmic reticulum.

• Receives instructions from nucleus in the form of mRNA on the specific order of amino acids to build a given protein

eukaryotic cells

Endomembrane system - modify, package and transport lipids and proteins

• Vesicles and peroxisomes - bud off from the endomembrane and serve as transport units for diverse materials

• Endoplasmic reticulum

• Golgi apparatus

• Mitochondria

ER and Golgi

The endoplasmic reticulum (ER) is a series of interconnected sacs and tubules that:

• modify proteins

• synthesize lipids

• The Golgi apparatus is a series of flattened membranes that receives proteins and lipids from the ER, which it then sorts, tags, packages and distributes.

mitochondria

The 'powerhouse' of the cell - it is the site of cellular respiration:

- Makes ATP (the cell's main energy-carrying molecule) from glucose and other nutrients- Uses oxygen and produces carbon dioxide as waste product.

• Contains its own DNA and ribosomes

plant cells uniqueness

Cell wall• Central vacuole• Plastids such as chloroplast

central vacuole

large, membrane-bound structure which stores water and can fill much of the cell

• plays a key role in regulating water concentration in the cell - releasing water under dry conditions and absorbing water under wet conditions(osmosis)

• Stores also nutrients, ions, and waste products

• Surrounded by tonoplast (membrane)

chloroplast

A type of plastid that stores chlorophyll and other pigments for photosynthesis

.• Pigments are stored in interconnected sacs - called thylakoids. They are often found in stacks called grana.

• Contains its own DNA and ribosomes

-Other plastids include: chromoplast (stores orange/yellow pigments) and amyloplast (stores starch)

cell wall

Middle lamella is a thin layer of pectin binding adjacent cells

• Primary cell wall occurs on the surface of all plant cells

- initially deposited on the surface of middle lamella

• Composed of cellulose microfibrils bundle together

• Rather thin and elastic, allowing for cell enlargement

• Only cell wall present in some cells

secondary cell wall

made of layers deposited inner to the primary wall

• Occurs as cell reach mature size

• Lignin is deposited together with cellulose - adding rigidity

• Thicker than primary wall

• As it grows, it pushes the cell membrane in - can lead to cell death

-Dead cells make over 90% of wood tissue!!!!

cell wall cond.

The orientation of cellulose microfibrils determine direction of cell enlargement

• Think of a spring - it can expand longitudinally but not laterally

• Plasmodesmata are pores which allow for communication between cells

Plant Growth

• Plants tissues are made of various types of cells that carry specific functions

• All tissues originate from meristematic tissue and later differentiate and specialize

• Plant tissue is totipotent - can regenerate the entire plant

• Meristems are regions of continuous cell division and growth located in different points of the plant.

There are 3 types:

• Apical meristems

• Lateral meristems

• Intercalary meristems (only in grasses)

apical meristems

Located at very end of stems (shoot apical meristems) and roots (root apical meristems)

• They produce 3 types of primary meristematic tissues:

• Protoderm – gives rise to epidermis

• Ground meristem – gives rise to ground tissue (photosynthetic, storage, support)

• Procambium – gives rise to vascular tissue(transport

lateral/secondary meristem

• Responsible for secondary growth– increase of girth

• Located in two regions:

• Vascular cambium (which arises from the procambium) - gives rise to vascular tissue

• Cork cambium (which arises from the pericycle and the cortex) -produces periderm (secondary dermal tissue)

3 types of primary meristematic tissue can be observed in seed embryo

main tissues of a plant can be grouped into 3 systems:

• Ground tissue system (e.g. mesophyll, pith)

• Vascular tissue system (xylem and phloem)

• Dermal tissue system (epidermis and periderm)

simple tissues

-Composed mostly of a single cell type.

-Perform essential functions, such as photosynthesis, support, storage, regulation

-There are 3 main types:

• Parenchyma

• Collenchyma

• Sclerenchyma

Parenchyma cells

• Usually spherical or elongated, but can have different shapes

• Thin primary cell walls, but may develop

lignified secondary walls

• Living cells perform many metabolic functions:

• Photosynthesis and respiration

• Storage and secretion

• Only type of cell that, when mature, can be reprogrammed to form other cell types!

• Tissue culture and wound healing

parenchyma tissue

Parenchyma cells can aggregate to form simple tissues such as:

• Cortex and pith: can serve a storage and support purposes

• Mesophyll: can serve a photosynthetic (palisade) and regulatory (spongy) role.

collenchyma

• Elongated, often containing chloroplast, and alive at maturity.

• Cell walls composed of alternating layers of pectin and cellulose - usually thicken at the corners!

• Strong and flexible

• Provides support to young stems and leaves -allowing for growth.

• Outermost cells of cortex - might aggregate into rights around the stem.

sclerenchyma

• Thick, lignified secondary cell walls. Dead atmaturity

• Two types of cells:• Fibers: long, narrow cells with thick, pitted cell walls tapered at the ends:

• Can aggregate into continuous cylinder around stems or form strands.

• Sclerids: can have many shapes (from simple stone shapes to highly branched).• Can form sheets (e.g. seed coat) or be in small clusters

complex tissue: vascular system

• Interconnected network of cells transversing the entire plant

• Composed of:

• Vessel elements and tracheids (water-conducting cells)

• Fibers (sclerenchyma cells for support)

• Living parenchyma cells (help load minerals in and out of conducting cells)

• Sieve-tube members (food conducting cells)

• Companion cells (specialized parenchyma cell)

complex tissue: epidermis

• Usually a single layer of cells in the outer part of the plant – as many as 6 layers in succulent plants

• Covered in cutin

• Complex tissue composed of:

• Epidermal cells – somewhat elongated, without chloroplast

• Guard cells: specialized

• Subsidiary cells

• Trichomes: outgrowths of one or more cells – in roots, they form root hairs. In leaves and stems, they can form protective structures

complex tissue: periderm

• A protective layer that forms in older stems and roots – replaces the epidermis

• A secondary tissue composed of:

• Phellem (cork) cells on the outside. Dead at maturity and with waxy suberin embedded in the cell walls

• Phellogen or cork cambium

• Phelloderm: parenchyma-like cells between the cork cambium and cortex.