Plastids and Chloroplast Structure
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Questions and Answers

What causes photorespiration to occur?

  • High levels of CO2
  • High temperatures only
  • Non-specificity of Rubisco (correct)
  • Low light intensity

Photorespiration results in energy production for the plant.

False (B)

What happens to the CO2/O2 ratio when the stomata are closed?

The CO2/O2 ratio decreases.

Photoinhibition is produced by very high light intensity that causes __________________ of the PSII system.

<p>over excitation</p> Signup and view all the answers

Match the following terms related to undesired functions in photosynthesis with their descriptions:

<p>Photorespiration = Waste of energy due to O2 fixation Photoinhibition = Damage caused by excessive light intensity Rubisco = Enzyme that binds CO2 and O2 Stomata = Regulate gas exchange in plants</p> Signup and view all the answers

What is the primary function of chromoplasts in plants?

<p>Pigment synthesis for color (D)</p> Signup and view all the answers

Chloroplasts are only found in flowering plants.

<p>False (B)</p> Signup and view all the answers

What type of pigments are primarily found in chloroplasts?

<p>Chlorophyll</p> Signup and view all the answers

Chromoplasts contain the carotenoid named ______, which contributes to the red color of tomatoes.

<p>lycopene</p> Signup and view all the answers

Match each type of plastid with its primary content:

<p>Chloroplast = Chlorophyll Chromoplast = Carotenoids Leukoplast = Starch or oil or proteins Elaioplast = Oils</p> Signup and view all the answers

Which of the following structures are chloroplasts bounded by?

<p>Two membranes (D)</p> Signup and view all the answers

Galactolipids found in chloroplast membranes are a type of carbohydrate.

<p>False (B)</p> Signup and view all the answers

The average size of chloroplasts is approximately ______ micrometers long.

<p>5 to 10</p> Signup and view all the answers

What is the primary function of the inner chloroplast membrane (ICM)?

<p>Regulate the transport of materials between the cytoplasm and the stroma (C)</p> Signup and view all the answers

The stroma contains ribosomes that are exclusively free and not attached to any membranes.

<p>False (B)</p> Signup and view all the answers

What is the most abundant enzyme on Earth involved in photosynthesis?

<p>Rubisco</p> Signup and view all the answers

The __________ is a complex of membranes and fluid matrix in chloroplasts that contains starch and lipid droplets.

<p>stroma</p> Signup and view all the answers

Match each chloroplast component with its function:

<p>Rubisco = CO2 fixation Plastoglobules = Thylakoid function support Nuclear genes = Protein encoding delivered post-translationally Transit peptide = Targets proteins to chloroplast subcompartments</p> Signup and view all the answers

Which proteins are encoded by chloroplast genes?

<p>Only 100 proteins (D)</p> Signup and view all the answers

Translocation complexes in chloroplasts are named TOC and TIC.

<p>True (A)</p> Signup and view all the answers

How many subcompartments are there in a chloroplast?

<p>Six</p> Signup and view all the answers

What is the primary function of thylakoids in chloroplasts?

<p>Photosynthesis (A)</p> Signup and view all the answers

Thylakoids are made up of 50% proteins and 40% lipids.

<p>True (A)</p> Signup and view all the answers

What are the small stacks of thylakoids called?

<p>Grana</p> Signup and view all the answers

The internal space of a thylakoid is known as the __________.

<p>lumen</p> Signup and view all the answers

Which of the following glycosphingolipids is largely found in the thylakoid membrane?

<p>Monogalactosyldiglyceride (C)</p> Signup and view all the answers

Match the types of pigments with their colors:

<p>Carotenoids = Orange Xanthophylls = Yellow Chlorophyll = Green</p> Signup and view all the answers

Which type of plastid is primarily responsible for storing starch?

<p>Amyloplast (C)</p> Signup and view all the answers

Which structure anchors chlorophyll in the lipid bilayer?

<p>Phytol tail (C)</p> Signup and view all the answers

Chloroplasts develop from proplastids upon exposure to suitable light intensity.

<p>True (A)</p> Signup and view all the answers

All chlorophylls have the same basic structure but differ by side groups on the porphyrin ring.

<p>True (A)</p> Signup and view all the answers

What is the function of protochlorophyll found in etioplasts?

<p>It is a chlorophyll precursor.</p> Signup and view all the answers

The _______ is an organelle that contains circular DNA and is bounded by two membranes.

<p>plastid</p> Signup and view all the answers

What type of plastid lacks genuine thylakoids and contains a prolamellar body?

<p>Etioplast (A)</p> Signup and view all the answers

What are proplastids, and where are they primarily found?

<p>They are colorless organelles found in young and dividing plant cells.</p> Signup and view all the answers

Match the plastid with its primary function:

<p>Chloroplast = Photosynthesis Amyloplast = Storage of starch Chromoplast = Pigment synthesis Etioplast = Light response preparation</p> Signup and view all the answers

The _______ are plastids that are involved in the production of pigments.

<p>chromoplasts</p> Signup and view all the answers

Which wavelengths of light do chlorophyll pigments primarily absorb?

<p>400 to 500 nm and 650 to 700 nm (A)</p> Signup and view all the answers

Chlorophyll reflects green light, which is why plants appear green.

<p>True (A)</p> Signup and view all the answers

What is the primary role of carotenoids in chloroplasts?

<p>Secondary light collectors and protect against excess energy.</p> Signup and view all the answers

Chemoautotrophs do not use light energy; they utilize __________ to produce organic compounds.

<p>energy of mineral compounds</p> Signup and view all the answers

Match the following types of organisms with their energy source:

<p>Photoautotrophs = Use light energy to produce organic compounds Chemoautotrophs = Use energy from mineral compounds Heterotrophs = Require organic compounds for nutrition Prokaryotic photoautotrophs = Have lamellar structures for photosynthesis</p> Signup and view all the answers

What is a key function of chloroplasts?

<p>Photosynthesis (D)</p> Signup and view all the answers

Prokaryotic photoautotrophs contain chloroplasts.

<p>False (B)</p> Signup and view all the answers

What are the main outputs of photosynthesis in chloroplasts?

<p>O2 and carbohydrates.</p> Signup and view all the answers

Flashcards

Plastids

Organelles found in plant cells that store various substances like oils, proteins, and pigments.

Elaioplasts

Plastids that store oils.

Proteoplasts

Plastids that store proteins.

Chromoplasts

Plastids that contain carotenoids, pigments responsible for yellow, red, and orange colors in plants.

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Carotenoids

Pigments found in chromoplasts that give plants their yellow, red, and orange hues.

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Lycopene

A type of carotenoid found in tomatoes, which is essential for their red color and is linked to health benefits.

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Chloroplasts

Organelles found in green plant tissues that contain chlorophyll, the pigment responsible for photosynthesis.

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Galactolipids

A type of glycolipid found in chloroplast membranes.

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Proplastids

Small, colorless organelles found in young plant cells that can develop into different types of plastids.

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Amyloplast

Type of plastid that stores starch.

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Etioplast

Type of plastid found in plants grown in the dark, containing a precursor to chlorophyll.

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Leucoplast

Enlarged colourless proplastids often found in internal tissues of the plant and epidermal cells, responsible for storage of various substances.

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Inner Chloroplast Membrane (ICM)

The inner membrane of a chloroplast, responsible for regulating the transport of materials between the cytoplasm and the stroma.

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Stroma

The fluid-filled main compartment of a chloroplast, contains enzymes, ribosomes, and DNA.

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Chloroplast Protein Import

The process of bringing proteins into the chloroplast.

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TOC Complex

A complex of proteins that facilitate the movement of proteins across the outer chloroplast membrane.

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TIC Complex

A complex of proteins that facilitate the movement of proteins across the inner chloroplast membrane.

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Transit Peptide

A specific amino acid sequence found at the beginning of a protein that signals its destination to the chloroplast.

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Rubisco (ribulose bisphosphate carboxylase)

A critical enzyme in photosynthesis that fixes carbon dioxide into organic molecules.

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Chloroplast DNA

A small, circular DNA molecule found within chloroplasts. It encodes some of the chloroplast proteins.

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Thylakoids

Disk-shaped structures within chloroplasts that are responsible for photosynthesis.

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Grana

Stacks of thylakoids in chloroplasts, resembling a pile of coins.

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Stroma Thylakoids

Individual thylakoids that extend laterally and interconnect the grana.

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Thylakoid Lumen

The internal space of a thylakoid.

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Photosynthetic Chain

A metabolic chain within thylakoid membranes responsible for photosynthesis.

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Monogalactosyl Diacylglycerol

A type of glycolipid abundant in thylakoid membranes, making them fluid.

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ATP Synthase Complex

Proteins embedded in the thylakoid membrane that are involved in ATP synthesis.

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Pigments in Thylakoid Membranes

Carotenoids, particularly xanthophylls, found in thylakoid membranes that absorb light energy.

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Photoautotrophs

Organisms that produce their own food using light energy and inorganic compounds like water and carbon dioxide.

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Chemoautotrophs

Organisms that produce their own food using the energy from inorganic compounds instead of light.

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Heterotrophs

Organisms that cannot produce their own food and rely on consuming other organisms for energy.

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Photosynthesis

The process plants use to convert light energy into chemical energy and store it as glucose, releasing oxygen as a byproduct.

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Chlorophylls

Pigments found in plants that absorb light energy, primarily blue and red wavelengths.

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Photorespiration

A process where chloroplasts consume O2 and release CO2, wasting energy. It happens when the enzyme Rubisco binds to O2 instead of CO2, due to low CO2/O2 ratio, often caused by closed stomata in hot, dry conditions.

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Photoinhibition

A process where high light intensity damages the photosystems in the photosynthesis chain, leading to the generation of toxic oxygen species. This disrupts the photosynthesis process and can kill the plant.

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Rubisco

The critical enzyme in photosynthesis that binds CO2 into organic molecules.

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What type of sugar is ribulose bisphosphate?

It's a five-carbon sugar (pentose) and a ketone.

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CO2/O2 ratio

The ratio of CO2 to O2 in the environment determines which gas will react with Rubisco.

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Study Notes

Plastids

  • Plastids are organelles found in higher plants and algae, characterized by two membranes enclosing a stroma.
  • Several types exist, including chloroplasts, amyloplasts, and chromoplasts.
  • Electron microscopy is needed to see their ultrastructure.
  • Proplastids are small, colorless, and found in young plant cells.
  • These eventually develop into various plastid types depending on environmental conditions.
  • Etioplasts are found in leaves grown in the dark.
  • They lack thylakoids, instead having a prolamellar body and flattened vesicles.
  • Leucoplastids are enlarged proplastids primarily involved in storage.
  • Amyloplasts store starch, frequently found in plant roots and other storage tissues.

Chloroplast Structure

  • Chloroplasts are abundant in leaf mesophyll cells, and in other green tissues of higher plants, mosses, and algae.
  • They contain pigments that give plants their green color.
  • Chloroplast morphology varies with species, cell type, and light intensity.
  • Higher plants typically have lens-shaped chloroplasts (2-4 µm wide, 5-10 µm long).
  • Chloroplasts are typically observed in the range of 20-40 per plant cell.
  • Chloroplast membranes include an outer and inner membranes, with an intermembrane space between them of 7-10 nm.
  • The stroma contains circular DNA, ribosomes, tRNA, enzymes for DNA replication, transcription, and translation, as well as light-absorbing pigments.
  • Thylakoid membranes are internal membrane sacs that form grana.

Chloroplast Functions

  • Chloroplasts are responsible for photosynthesis: capturing light energy, fixing CO2 and producing carbohydrates in plants.
  • The process is the inverse of cellular respiration.
  • Chloroplasts also store carbohydrates as starch, and create other types of sugars.
  • Some Chloroplasts carry out photorespiration where it leads to O2 consumption and CO2 release which is a wasteful process.
  • Photoinhibition is another undesired function where too much light damages the photosystems.

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