Botany 301 (UNIT 1)

The Plant Cell

What are the primary organs of a plant?

Roots, shoots, and Leaves

What are the two main functions of roots?

Anchorage and absorption of water and nutrients.

Which vascular tissue transports water and minerals from the roots?

Xylem

Which vascular tissue transports sugars (photosynthates) from the leaves to the rest of the plant?

Phloem

Xylem vs Phloem

Xylem: moves water and minerals (mostly upwards)

Phloem: moves sugars (photosynthates) through out the plant [source → sink]

Besides transporting materials, what is another major function of stems?

Provide structural support and connect the vascular tissues between roots and leaves.

What three ingredients are needed for photosynthesis?

CO2, H2O, & Sunlight

What two products are produced during photosynthesis?

Glucose and Oxygen

Why is photosynthesis considered the most important chemical reaction for life on Earth?

Because it converts sunlight into chemical energy, produces oxygen, and creates the organic molecules that support nearly all life.

What four major classes of organic molecules are ultimately produced from photosynthesis?

• Carbohydrates

• Proteins

• Lipids

• Nucleic acids

Why are proteins especially important in living organisms?

Many proteins are enzymes that regulate nearly all biochemical reactions (photosynthesis, cellular respiration, & DNA replication, etc.).

Name five ways plants are important to humans.

Examples:

• Oxygen

• Food

• Medicine

• Building materials

• Fuel

• Environmental services

• Cultural connection

• aesthetic value

• Happiness!

Why is oxygen produced during photosynthesis essential for humans?

Photosynthesis releases oxygen into the atmosphere. Most living organisms (humans) need this oxygen to survive, and some of it forms the ozone layer, which protects Earth from harmful UV radiation.

Give two examples of ecosystem services provided by plants.

Examples:

• Carbon storage

• Water filtration

• Prevent soil erosion

• Habitat for wildlife

• Shoreline protection

A forest is removed from an area.

Name three ecosystem functions that may be negatively affected.

Possible answers:

• Less carbon storage

• Increased erosion

• Habitat loss

• Reduced biodiversity

• Poorer water quality

Name four major threats facing plants today.

Examples:

• Habitat loss

• Pollution

• Climate change

• Population growth

• Altered fire regimes

How are plants organized from smallest to largest?

Cell → Tissue → Organ → Organ System → Organism

Every plant organ contains which three tissue systems?

• Dermal tissue system

• Ground tissue system

• Vascular tissue system

What is any given tissue made of?

one or more cell types that work together to perform a specific function.

How are plant organs, tissues, and cells related?

Each plant organ (roots, stems, and leaves) contains three tissue systems (dermal, ground, and vascular), and each tissue system is made of one or more specialized cell types.

Which four structures are found in plant cells but not animal cells?

• Cell wall

• Large central vacuole

• Plastids

• Plasmodesmata

Which plant cell structure stores water and helps maintain cell pressure?

The large central vacuole stores water and helps maintain turgor pressure, which supports the plant.

What is the structure of a plant cell vacuole?

A vacuole is a large compartment filled with aqueous (water-based) contents and surrounded by a single membrane called the tonoplast.

What are the seven major functions of the vacuole?

The vacuole functions in:

• Storage

• Defense

• Reproduction (pigmentation)

• Protection

• Recycling cellular materials

• Cell growth

• Support (turgor pressure)

What types of substances are commonly stored in the vacuole?

The vacuole stores:

• Amino acids

• Proteins

• Sugars

• Organic acids

• Inorganic ions (Ca²⁺, K⁺, Cl⁻, Na⁺, HPO₄²⁻)

How does the vacuole help defend the plant?

The vacuole can store toxic defensive chemicals such as alkaloids, terpenes, phenolics, and calcium oxalate crystals (druses and raphides) that help protect the plant from herbivores.

Give four examples of alkaloids found in plant vacuoles.

• Nicotine

• Caffeine

• Cocaine

• Tropane alkaloids

How does the vacuole contribute to pollination?

The vacuole stores water-soluble pigments (anthocyanins) that give flowers bright colors and attract pollinators.

Besides attracting pollinators, what else do anthocyanins help protect?

Anthocyanins protect young buds and aging leaves from UV damage and may also reduce insect attraction because many insects do not see red well.

How does the vacuole contribute to plant growth?

As the vacuole enlarges and fills with water, it causes the cell to expand, making it an important driver of cell enlargement.

Why do plants wilt when they lose water?

Water leaves the vacuoles, causing cells to lose turgor pressure, which makes the plant wilt.

What is a plastid?

A plant organelle that performs specialized functions such as photosynthesis, pigment production, storage, and the synthesis of important molecules.

Common types of plastids include chloroplasts, chromoplasts, and leucoplasts(such as amyloplasts, proteinoplasts, and elaioplasts).

Different plastids carry out different functions and all develop from proplastids.

What structural features are shared by all plastids?

Plastids:

• Have a double membrane

• Contain their own DNA

• Divide independently of the rest of the cell

• Develop from proplastids

According to the endosymbiotic theory, how did plastids originate?

Plastids evolved when a photosynthetic cyanobacterium was engulfed by a eukaryotic cell and became a permanent endosymbiont instead of being digested.

Why was the origin of plastids such an important event in plant evolution?

It gave plants the ability to photosynthesize, allowing them to produce their own food and paving the way for the evolution of modern plants.

Name five important functions of plastids.

Examples include:

• Photosynthesis

• Pigmentation

• Amino acid synthesis

• Lipid synthesis

• Storage of lipids, carbohydrates, and proteins

• Gravity sensing

• Regulation of stomata

Can one plant cell contain more than one type of plastid?

Yes. A single cell may contain multiple plastid types, and plastids can differentiate from one type into another.

Which plastid carries out photosynthesis?

Chloroplasts:

• Contain chlorophyll a and b

• Produce sugars through photosynthesis

What is the function of chromoplasts?

Chromoplasts contain carotenoids and xanthophylls that provide yellow, orange, and red pigmentation and help protect against UV damage.

Which leucoplast has this primary function: Starch production and storage; gravity perception

Amlyoplast

Which leucoplast has this primary function: Protein storage

Proteinoplast (Aleuroplast)

Which leucoplast has this primary function: Oil storage

Elaioplast

What are etioplasts?

Etioplasts are plastids that develop in the dark and contain lamellar bodies that later develop into thylakoids when exposed to light.

What are gerontoplasts?

Gerontoplasts develop from chloroplasts during leaf senescence and are involved in the break down of photosynthetic pigments as leaves prepare to fall.

What is senescence?

Senescence is the series of changes that occur after an organism or plant organ reaches maturity, often leading to aging and eventual death of that organ.

What is abscission?

Abscission is the dropping of plant organs, such as leaves, flowers, or fruit.

Why do leaves change color in autumn?

As chlorophyll breaks down, underlying pigments become visible. Many plants also increase production of carotenoids, xanthophylls, and anthocyanins during senescence.

What are the five major theories explaining the adaptive advantage of autumn leaf coloration?

• Photoprotection Theory

• Anti-Herbivory Theory

• Co-evolution (Signaling) Theory

• Nutrient Recovery Efficiency Theory

• Detoxification Hypothesis

What is the Photoprotection Theory of autumn leaf coloration?

Anthocyanins protect leaves from excess light and fluctuating temperatures during nutrient resorption, allowing the plant to recover nutrients like nitrogen and phosphorus more efficiently before leaf drop.

What is the Anti-Herbivory Theory of autumn leaf coloration?

Bright autumn colors, especially red, may warn herbivorous insects that the tree has strong chemical defenses, reducing insect damage and overwintering pests.

What is the Co-evolution (Signaling) Theory of autumn leaf coloration?

Bright leaf colors may signal to insects that a tree is healthy and well-defended, discouraging colonization and reducing future insect infestations.

What is the Nutrient Recovery Efficiency Theory of autumn leaf coloration?

Anthocyanins may slow leaf senescence, giving the plant more time to recover valuable nutrients before the leaves are shed.

What is the Detoxification Hypothesis of autumn leaf coloration?

Anthocyanins help neutralize harmful byproducts produced during leaf senescence, protecting leaf tissues from oxidative stress while nutrients are recovered.

What are the major functions of the plant cell wall?

• Provides structural support

• Prevents the cell from bursting

• Determines cell shape and size

• Acts as a selective barrier

• Senses and responds to environmental stress

• Stores water and regulatory molecules

What are the four main components of the plant cell wall?

• Middle lamella

• Primary cell wall

• Plasmodesmata

• Secondary cell wall (in some cells)

How is the plant cell wall formed?

The cell wall is deposited in stages:

• Primary cell wall – formed first during cell expansion.

• Secondary cell wall – deposited after cell growth is complete (often becomes lignified).

What is the middle lamella and what is its function?

The middle lamella is a pectin-rich layer that acts like glue, holding adjacent plant cells together.

What happens to the middle lamella as fruit ripens?

Enzymes break down pectin, weakening the middle lamella so cells separate more easily, causing fruit to soften.

Why is pectin commonly used to make jams and jellies?

Pectin is a soluble dietary fiber that forms a gel when combined with sugar and heated, giving jams and jellies their thick consistency.

What is cellulose?

Cellulose is a β-1,4 glucan, a linear polymer of glucose molecules and the most abundant organic molecule on Earth. It is the main structural component of the primary cell wall.

How does cellulose help determine the shape of a plant cell?

As turgor pressure pushes outward, strong cellulose microfibrils resist expansion and guide the cell into its final shape.

How are cellulose microfibrils produced?

Cellulose synthase enzymes in the plasma membrane produce cellulose microfibrils. These microfibrils are laid down in the same direction as microtubules, helping determine the strength and shape of the cell wall.

What are the functions of hemicelluloses, pectins, proteins, and water in the primary cell wall?

• Hemicelluloses → Cross-link cellulose microfibrils.

• Pectins → Form the hydrated matrix and help bind cells together.

• Proteins → Modify the wall and help defend against pathogens.

• Water → Moves through the wall and contributes to hydration.

What are plasmodesmata?

Plasmodesmata are cytoplasmic channels that pass through cell walls, connecting neighboring plant cells and allowing communication and transport between them.

Name the three pathways by which water moves between plant cells.

• Apoplast – Through cell walls and intercellular spaces.

• Symplast – Through the cytoplasm via plasmodesmata.

• Transmembrane – Across plasma membranes from cell to cell.

When is the secondary cell wall formed?

After the cell has finished growing. It is deposited inside the primary cell wall and often becomes lignified.

How does the secondary cell wall differ from the primary cell wall?

• Is rich in cellulose and hemicelluloses

• Usually contains lignin

• Lacks pectins and proteins

• Is deposited after cell growth is complete

What are the major functions of lignin?

• Strengthens the cell wall

• Makes wood waterproof

• Resists degradation

• Prevents further cell growth and division once deposited

Are all secondary cell walls lignified?

No. Most are lignified, but some, such as cotton fibers, have non-lignified secondary cell walls.

What are pits in the secondary cell wall?

Pits are areas where only the primary cell wall remains between adjacent cells, allowing transport and communication.