Photoreceptors and Plant Responses

A type of receptor that responds to light.

A type of photoreceptor that absorbs blue light, which is used in processes like phototropism and circadian rhythm.

A type of photoreceptor that absorbs red light, which is used in processes like seed germination and flowering.

A plant pigment that acts as a molecular light switch, changing between two forms to trigger different responses.

The inactive form of phytochrome, which absorbs red light.

The active form of phytochrome, which absorbs far-red light.

The difference in electrical charge between the inside and outside of a cell membrane.

A rapid change in the electrical potential across the cell membrane, usually driven by the movement of ions like calcium, potassium, and chlorine.

The process where light energy is used to convert carbon dioxide (CO2) and water (H2O) into glucose (sugar) and oxygen (O2). It occurs in the chloroplasts of plants and algae.

A series of reactions that use the chemical energy from ATP and NADPH to convert CO2 into glucose. This process occurs in the stroma of chloroplasts.

A protein that catalyzes the first step of carbon fixation in the Calvin cycle. It binds to CO2 and RuBP (ribulose bisphosphate) to form an unstable six-carbon compound.

A series of membrane-embedded protein complexes that transfer electrons to pump protons (H+) across a membrane, generating a proton gradient used to produce ATP.

The reduction of NADP+ to NADPH by using electrons from Photosystem I (PSI). NADPH is a crucial reducing agent used in the Calvin cycle.

The first stage of photosynthesis, where light energy is captured by chlorophyll and used to create ATP and NADPH. It occurs in the thylakoid membrane of chloroplasts.

A pigment that absorbs light energy, primarily in the red and blue wavelengths. It is essential for photosynthesis.

A small, flattened sac-like structure in chloroplasts where chlorophyll is located. It's where light-dependent reactions occur.

A rigid structure that surrounds plant cells and provides support, shape, and protection. It's composed of cellulose microfibrils.

A unbranched polysaccharide carbohydrate that is a major component of the cell wall. It provides strength and support.

The process by which plants take in water from the soil through their roots. This is needed for photosynthesis and other cellular processes.

The outermost layer of a plant cell, made of cellulose, hemicellulose, and pectin. It provides structural support and allows for the passage of water and nutrients.

A thicker, more rigid layer that forms inside the primary cell wall in some plant cells. It's primarily composed of cellulose and lignin, giving it strength and waterproofing properties.

A thin layer rich in pectin that glues adjacent plant cells together, connecting their primary walls.

Tiny pores that connect the cytoplasm of neighboring plant cells, allowing for the passage of ions, molecules, and signals.

Plant tissues that are responsible for storage, photosynthesis, and support.

The outer protective layer of the plant that covers leaves, stems, and roots. It primarily serves to protect the plant from damage and pathogens.

Plant tissue composed of specialized cells that are responsible for the transport of water and nutrients throughout the plant.

The region of undifferentiated cells in plants where new growth occurs, responsible for increasing plant length.

The movement of water across a semipermeable membrane from a region of high water potential to a region of low water potential.

The potential energy of water, determined by the concentration of solutes and pressure.

A waxy layer in the root endodermis that blocks the apoplastic movement of water and minerals into the vascular tissues.

The movement of water through the xylem from the roots to the leaves, driven by the difference in water potential between the two ends of the xylem.

The force of attraction between water molecules, due to hydrogen bonds.

The force of attraction between water molecules and other substances.

Tiny pores on the surface of leaves that open and close to regulate gas exchange and water loss.

Cells that surround stomata and control their opening and closing.

Auxin promotes the release of H+ ions into the cell wall, which lowers the pH and activates expansins. Expansins break down hydrogen bonds between polysaccharides in the cell wall, allowing the cellulose microfibrils to slide past each other. This enables cell expansion when there's sufficient turgor pressure.

Photosynthesis takes place in chloroplasts found in the mesophyll tissue of leaves. Chloroplasts have an outer membrane and an inner membrane with a third membrane called the thylakoid membrane. The thylakoid membrane houses chlorophyll pigments, which are crucial for capturing light energy. Stacks of thylakoids form grana, and the fluid-filled region between the thylakoids and the inner membrane is known as the stroma.

The light reactions of photosynthesis convert light energy into chemical energy (ATP and NADPH). They take place in the thylakoid membrane and involve photosystems II and I.

The Calvin cycle is a light-independent process that uses the energy from ATP and NADPH generated in the light reactions to convert carbon dioxide into glucose. This process occurs in the stroma.

Light-harvesting complexes capture photons and pass the energy to chlorophyll a molecules in the reaction-center complex. The energy excites an electron in the chlorophyll a molecule, causing it to jump to a higher energy level and be accepted by a primary electron acceptor.

During the electron transport chain, electrons move through different protein complexes (Pq, cytochrome complex, Pc) within the thylakoid membrane. This process pumps protons into the thylakoid lumen, creating a proton gradient. The energy stored in this gradient is then used by ATP synthase to generate ATP from ADP and inorganic phosphate.

Chemiosmosis is the process of using the potential energy stored in the proton gradient across the thylakoid membrane to synthesize ATP. ATP synthase, an enzyme embedded in the thylakoid membrane, harnesses this energy to convert ADP and inorganic phosphate into ATP.

Both chloroplasts and mitochondria utilize chemiosmosis to generate ATP. However, in chloroplasts, chemiosmosis occurs across the thylakoid membrane and involves proton movement into the thylakoid lumen, whereas in mitochondria, it takes place across the inner membrane and involves proton movement into the intermembrane space.