2.1 Plant 2.1 Plant Cells, Cells,

Tissues, Tissues, and and

OrgansOrgans

cell specializationcell specialization = when young cells develop from = when young cells develop from similar cells into ones that have specific functionssimilar cells into ones that have specific functions

Occurs in multicellular organismsOccurs in multicellular organisms Cell differentiationCell differentiation is the development stage in a is the development stage in a

young organism when specialized cells formyoung organism when specialized cells form Genes produce the proteins that cause cells to become Genes produce the proteins that cause cells to become

specialized into a bone cell, nerve cell, muscle cell, ...specialized into a bone cell, nerve cell, muscle cell, ... all cells contain the same DNAall cells contain the same DNA certain genes “turn on” in one cell type, but not in otherscertain genes “turn on” in one cell type, but not in others

New cells come from pre-existing cells by New cells come from pre-existing cells by mitosismitosis (& (& cytokinesis), but they are not necessarily going to cytokinesis), but they are not necessarily going to perform the same functionperform the same function

Cell SpecializationCell Specialization

In all multicellular plants & animals: groups of specialized cells form tissues groups of tissues form organs groups of organs form systems

In plants, unspecialized cells are called In plants, unspecialized cells are called meristematic meristematic cellscells

In animals, unspecialized cells are called In animals, unspecialized cells are called stem cellsstem cells Meristematic cells are sometimes called ‘permanent Meristematic cells are sometimes called ‘permanent

embryos’, because unlike many animal stem cells, they embryos’, because unlike many animal stem cells, they can produce cells that will become new tissues & organs can produce cells that will become new tissues & organs at any point in a plant’s lifeat any point in a plant’s life in humans, true undifferentiated stem cells exist only as a fetusin humans, true undifferentiated stem cells exist only as a fetus

Plant: meristematic cells tissues organs systems

Animal: stem cells tissues organs systems

PlantAnimal

Meristematic Cells form TissuesMeristematic Cells form Tissues

Meristematic cells are constantly producing Meristematic cells are constantly producing new cellsnew cells these new cells become specialized to form tissuesthese new cells become specialized to form tissues

Types of plant tissues:Types of plant tissues:

1. Dermal tissue1. Dermal tissue

2. Ground tissue2. Ground tissue

3. Vascular tissue3. Vascular tissue

Figure 2.3 on p.58

Types of Plant TissuesTypes of Plant Tissues

1.1. Dermal tissueDermal tissue outermost part outermost part Made of epidermal cellsMade of epidermal cells These cells act as a barrier by:These cells act as a barrier by:

protecting the more delicate inner tissuesprotecting the more delicate inner tissues controlling the exchange of materialscontrolling the exchange of materials

2. 2. Ground tissueGround tissue middle layer middle layer Made of photosynthesizing cells & support cells Made of photosynthesizing cells & support cells

3. 3. Vascular tissueVascular tissue innermost tissue innermost tissue Made of phloem cells & xylem cellsMade of phloem cells & xylem cells

phloem cells transport nutrients like water & sugar phloem cells transport nutrients like water & sugar throughout the plantthroughout the plant

xylem cells provide physical supportxylem cells provide physical support

Replacing Specialized CellsReplacing Specialized Cells Cells, tissues, and organs of multicellular animals like humans Cells, tissues, and organs of multicellular animals like humans

form as embryos inside the wombform as embryos inside the womb while some of the cells can be replaced, organs have to last for life!while some of the cells can be replaced, organs have to last for life! mammals cannot regenerate organsmammals cannot regenerate organs

Unlike many animals, plants can replace cells, tissues and Unlike many animals, plants can replace cells, tissues and organs throughout their lives organs throughout their lives they can produce new cells which will become organs like leaves, they can produce new cells which will become organs like leaves,

roots, & stemsroots, & stems

Bud Bud = cluster of meristematic cells that often specialize to = cluster of meristematic cells that often specialize to form leaf or flower organsform leaf or flower organs

Most of a plant’s growth takes place at the terminal bud Most of a plant’s growth takes place at the terminal bud see Figure 2.4 and 2.5 on p. 59 see Figure 2.4 and 2.5 on p. 59 terminal bud produces the plant hormone terminal bud produces the plant hormone auxinauxin which ‘holds back’ which ‘holds back’

growth in other placesgrowth in other places

Plant OrgansPlant OrgansTissues working together to form a leaf, one plant organ

How many plant organs How many plant organs can you identify in the can you identify in the diagram to the right?diagram to the right?

1.1. LeafLeaf

2.2. StemStem

3.3. RootsRoots

4.4. (Flower)(Flower)

reproductive organ

reproductive organ

The LeafThe Leaf Its most important job is to provide a large surface area Its most important job is to provide a large surface area

for photosynthesis to take placefor photosynthesis to take place

Upper surfaceUpper surface Made of a layer of dermal tissue called the epidermisMade of a layer of dermal tissue called the epidermis Epidermal cellsEpidermal cells secrete a waxy cuticle (top layer) that: secrete a waxy cuticle (top layer) that:

helps reduce water evaporation off of leafhelps reduce water evaporation off of leaf protects the leaf so it can perform its primary function, protects the leaf so it can perform its primary function,

photosynthesisphotosynthesis sunlight passes through epidermal cells to sunlight passes through epidermal cells to

photosynthesizing cellsphotosynthesizing cells

Middle surfaceMiddle surface Made of mesophyll tissue (a special type of ground tissue), Made of mesophyll tissue (a special type of ground tissue),

which is composed of 2 types of cells:which is composed of 2 types of cells: palisade cellspalisade cells, which are specialized to perform most of the , which are specialized to perform most of the

photosynthesis in the leafphotosynthesis in the leaf spongy parenchyma cells, spongy parenchyma cells, which form a loose network of open which form a loose network of open

spaces (like a sponge), where gases for photosynthesis can be spaces (like a sponge), where gases for photosynthesis can be contained (COcontained (CO22, H, H22O, OO, O22))

xylemxylem and and phloemphloem cells are arranged in bundles that form cells are arranged in bundles that form veins to help the palisade cells conduct photo. & cell resp.veins to help the palisade cells conduct photo. & cell resp. xylem delivers water for photosynthesisxylem delivers water for photosynthesis phloem picks up sugars that have been produced in the palisade phloem picks up sugars that have been produced in the palisade

cells to transport to the rest of the plant (in the form of sap)cells to transport to the rest of the plant (in the form of sap)

Lower surface (underside)Lower surface (underside) Also made of a layer of Also made of a layer of

dermal tissue, but the cells dermal tissue, but the cells are differentare different

Guard cellsGuard cells allow gases to allow gases to move in & out of the leafmove in & out of the leaf

these cells have special pores these cells have special pores called called stomatastomata

stomata are connected to the stomata are connected to the open spaces in the mesophyllopen spaces in the mesophyll

transpiration happens through transpiration happens through these poresthese pores

COCO22 enters, H enters, H22O and OO and O22 leave leave

See Figure 2.8 on p. 61

transpiration = evaporation of water from the leaves

Located in palisade cells in the mesophyllLocated in palisade cells in the mesophyll Where photosynthesis takes placeWhere photosynthesis takes place Palisade cells contain Palisade cells contain thylakoids thylakoids

thylakoidsthylakoids = sacs that contain chlorophyll to trap light = sacs that contain chlorophyll to trap light when thylakoids are stacked, they are called when thylakoids are stacked, they are called granum granum

(plural are grana)(plural are grana)

Chloroplasts: the Leaf’s Key OrganelleChloroplasts: the Leaf’s Key Organelle

See Figure 2.9 on p. 63

A 3D look at a leaf organ

Has 2 main jobs:Has 2 main jobs: supportsupport transportation of water, nutrients and sugarstransportation of water, nutrients and sugars

Xylem & phloem tissues are found here Both are made of vertically stacked tubes

Most of a plant’s xylem tissue is found in the stem when xylem cells die, they provide long, fibrous ‘pipes’

that allow water to be transported easily Phloem’s cell walls are porous to allow materials to

move easily between phloem & neighbouring cells Xylem & phloem are grouped together in vascular

bundles

The StemThe Stem

See Figure 2.10 on p. 64

Also has 2 main jobs:Also has 2 main jobs: anchor the plant to the groundanchor the plant to the ground allow for water and minerals to be taken out of the soilallow for water and minerals to be taken out of the soil

In some plants, the roots act like a storage area for In some plants, the roots act like a storage area for starch & mineralsstarch & minerals

Special cells in the roots called Special cells in the roots called cortex cellscortex cells serve to serve to store starch (long chains of glucose)store starch (long chains of glucose)

Endodermis tissueEndodermis tissue controls water and mineral flow to controls water and mineral flow to vascular tissuesvascular tissues

Pericycle tissuePericycle tissue surrounds the xylem and phloem surrounds the xylem and phloem it allows roots to branch outit allows roots to branch out

The RootsThe Roots

See Figure 2.11 on p. 65

Cross section of an Actual RootCross section of an Actual Root

Also see Figure 2.12 on p. 65

1. Taproot1. Taproot One main root that grows One main root that grows

larger and thicker than the restlarger and thicker than the rest Allows plant to reach far Allows plant to reach far

underground for waterunderground for water ex: dandelion, thistleex: dandelion, thistle

2. Fibrous root2. Fibrous root Thin, hair-like rootsThin, hair-like roots Allows plant to absorb water Allows plant to absorb water

from near the surface of the from near the surface of the soilsoil

Help prevent erosionHelp prevent erosion ex: grass, yarrowex: grass, yarrow

Types of RootsTypes of Roots

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