chapter 4 Plant Cell

Cell

Basic structural and functional unit of living organisms.

Microscopic cells

Most plant and animal cells; too small to be seen with the unaided eye.

Macroscopic cells

Cells large enough to be seen without a microscope.

Micron (μ)

Unit for microscopic measurements; 1 … = 0.001 millimeter.

Prokaryotic cells

Lack a nucleus and membrane-bound organelles; DNA is scattered in the cytoplasm; all are single-celled (e.g., eubacteria and archaebacteria). Classification of Cells (by Structure)

Eukaryotic cells

Have a nucleus with a membrane; DNA is in chromosomes; contain membrane-bound organelles like mitochondria, ER, and Golgi bodies. Classification of Cells (by Structure)

Autotrophs

"Self-feeders"; make their own food using light (photosynthesis) or chemical energy (chemosynthesis). Classification of Cells (by Food Source)

Heterotrophs

Organisms that get energy by consuming other organisms. Classification of Cells (by Food Source)

Cell Wall

Outermost part of most plant cells (absent in some seed plant sperm); made mostly of cellulose.

Cellulose

Crystallizes into strong microfibrils that give strength to the wall. Cell Wall

Hemicelluloses

Help pack cellulose microfibrils; produced by dictyosomes and delivered via vesicles. Cell Wall

Middle Lamella

Adhesive layer between adjacent cells; mainly made of pectic substances. Cell Wall

Primary wall

Present in all plant cells. Cell Wall

Secondary wall

Thicker, contains lignin; forms between the primary wall and protoplast in some cells. Cell Wall

Cell walls (function)

Permanent, not degraded; help maintain shape and resist deformation. Cell Wall

Plasma Membrane

Semi-permeable outer covering; lets beneficial substances in, blocks harmful ones. Also known as Plasmalemma

Molecular pumps

Actively transport substances in/out of the cell. Plasma Membrane

proteins

Plasma Membrane is Made of a double phospholipid layer with …

Cytoplasm

Largest part of the cell; contains organelles and inclusions; enclosed by the plasma membrane.

Mitochondria

Site of cellular respiration; breaks down sugars, starches, and amino acids to release energy.

ATP (Adenosine Triphosphate)

High-energy compound produced in mitochondria.

Cristae

Inner membrane folds that increase surface area for enzymatic activity. Mitochondria

Matrix

Liquid inside mitochondria where chemical reactions occur. Mitochondria

permeable

Inner membrane for ATP synthesis; outer membrane is smooth and … (Mitochondria)

Ionic pumps/channels

Assist in chemiosmosis.

Mitochondrial DNA and ribosomes

Different from cytoplasmic ones; mitochondria can divide and grow.

100 to 1000

Number per cell, depending on energy needs. (Mitochondria)

Dictyosomes

Stack of disk-shaped sacs near the Endoplasmic Reticulum.

Forming face

Receives vesicles from Endoplasmic Reticulum. Dictyosomes.

Dictyosomes Functions

Modify materials, synthesize new ones; release vesicles from maturing face.

Secretory vesicles

Exported or used for repair or lysosome formation. Dictyosomes

Rough Endoplasmic Reticulum

Has ribosomes; involved in protein synthesis.

Smooth Endoplasmic Reticulum

No ribosomes; involved in lipid synthesis.

Proteins

… are sorted and modified as they pass through Endoplasmic Reticulum.

Ribosomes

Free in cytoplasm or attached to ER; responsible for protein synthesis.

Animal cells

Especially liver cells, have more ribosomes than plant cells.

Microbodies

Spherical structures (0.5–1.5 μm) in the cytoplasm.

Peroxisomes

Detoxify hydrogen peroxide and photosynthesis by-products.

Glyoxysomes

Found only in plants; convert stored fats to sugars; important in germination of oily seeds.

Catalase

Enzyme that detoxifies H₂O₂ into water and oxygen.

Plastids

Have inner/outer membranes, stroma, circular DNA, and ribosomes.

Chromoplasts

Colored plastids (e.g., chloroplasts).

Leucoplasts

Unpigmented (e.g., amyloplasts).

Chloroplasts

Site of photosynthesis.

Amyloplasts

Store starch.

chloroplasts, amyloplasts

Plastids Contribute to photosynthesis directly (?) or indirectly (?).

Microtubules

Thin hollow tubes under the membrane; help add cellulose to the wall; present in dividing cells. Cytoskeleton Components

Microfilaments

Long protein bundles; involved in cyclosis (cytoplasmic streaming); form flexible framework with microtubules. Cytoskeleton Components

Vacuoles

Most common in plants are water … filled with cell sap.

Young cells – Cells that have smaller vacuoles.

Mature cells – Cells that has 1–2 large central vacuoles, can occupy over 90% of cell volume.

Nucleus

Control center of the cell; contains chromatin.

Nuclear Envelope

Double membrane with pores.

Nucleoplasm

Granular fluid inside the nucleus.

Chromatin

Dark-staining bodies with genetic material.

Nucleolus

Site of rRNA synthesis; rRNA combines with proteins to form ribosomes.

Water

Essential for transport (diffusion, osmosis, imbibition, capillarity, absorption, transpiration).

Diffusion

Passive movement of molecules from high to low concentration; leads to equilibrium.

Osmosis

Movement of water across a semi-permeable membrane from low solute (high water) to high solute (low water).

Aquaporins

Proteins that form channels to speed up water transport.

Plasmolysis

Water leaves the cell in hypertonic solution; protoplast shrinks from wall.

Incipient plasmolysis

Initial stage of protoplast detachment.

Turgid cell

In hypotonic solution, cell swells with water.

Flaccid cell

Lost turgidity; cannot support plant → wilting.

Imbibition

Diffusion where water is attracted to cellulose microfibrils, causing swelling and loosening of walls.

Water potential (ψω)

Predicts water movement; depends on osmotic potential (ψο) and pressure potential (ψρ).

Water Potential Equation

ψω = ψρ + ψο

Osmotic Potential (ψο)

Due to solute concentration; always zero or negative.

Pressure Potential (ψρ)

Pressure by the wall on protoplast; always positive.

Higher Water potential tissue

Loses water → decreases in mass and volume.

Lower Water potential tissue

Gains water → increases in mass and volume.

Elasticity

Ability to resist deformation; helps maintain turgor and water potential balance.

Turgor Pressure

Internal pressure from water; important for structure.

Young cells

More elastic. Elasticity of Cell Walls

Mature cells

Less elastic due to thicker secondary walls. Elasticity of Cell Walls

rigid mature cells

Camote tops, malunggay, gabi, mustard leaves are examples of …