Q.Product of photosynthesis is transported from the leaves to various parts of the plants and stored in some cell before being utilised. What are the cells/ tissues that store them?
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Phloem Elements – The Plant's Food Highway
Think of a tree. The leaves make food (sugar) through photosynthesis. That food has to travel down to the roots, and also up to growing buds and fruits. Water moves up through xylem, but sugar moves through a completely different system: phloem.
Phloem is the living tissue that transports organic nutrients — mainly sucrose — from where they are made (source) to where they are needed (sink). Unlike xylem, which is mostly dead at maturity, phloem cells stay alive and work together like a team.
The Four Cell Types of Phloem
Phloem is not one kind of cell. It is a composite tissue made of four distinct elements, each with a specific job.
1. Sieve Tube Elements – The Conduit
These are the actual pipes for sugar transport. They are elongated cells arranged end-to-end, forming long sieve tubes. The end walls have clusters of pores, looking like a sieve — hence the name.
Sieve tube elements lose their nucleus, ribosomes, and most organelles at maturity. They are alive but dependent on companion cells for metabolic support. Without a nucleus, they cannot make proteins or manage their own life.
The cytoplasm of adjacent sieve tube elements is connected through the sieve pores, allowing a continuous stream of sap to flow.
2. Companion Cells – The Manager
Each sieve tube element has one or more companion cells right next to it, connected by numerous plasmodesmata. The companion cell has a dense cytoplasm and a prominent nucleus.
The companion cell controls the life of the sieve tube element. It supplies ATP, proteins, and signalling molecules. It also loads sugar into the sieve tube against a concentration gradient — an active process that drives the entire transport.
Without companion cells, sieve tubes would die within hours.
3. Phloem Fibres – The Support
These are sclerenchyma cells — long, thick-walled, and dead at maturity. They provide mechanical strength to the phloem tissue. In some plants, like jute and flax, phloem fibres are commercially important for making ropes and textiles.
Phloem fibres are not involved in transport. They are purely structural. In primary phloem, they are often absent or few; in secondary phloem, they can form prominent bundles.
4. Phloem Parenchyma – The Storage
These are living, thin-walled cells that store starch, fats, and other organic compounds. They also help in lateral transport of solutes within the phloem. Unlike companion cells, they are not directly connected to sieve tubes.
How They Work Together
The flow of sap in phloem is explained by the pressure flow hypothesis. Companion cells actively pump sucrose into sieve tubes at the source (e.g., leaves). This makes the sap hypertonic, drawing in water from xylem. The increased pressure pushes the sap towards sink regions (roots, fruits), where sucrose is unloaded and water returns to xylem.
Pressure Flow Model
Sourceactive loadingHigh pressurebulk flowSinkunloadingLow pressure …
The sugars and other organic substances made in the leaves during photosynthesis are carried through the phloem (as sieve-tube conduction) to other parts of the plant, and along the way, and at their destination, they are held in storage mainly by parenchyma cells — in particular the phloem parenchyma that lies alongside the conducting sieve tubes, as well as the parenchyma cells of the cortex, pith and medullary rays in stems and roots. …
Photosynthate is moved through the phloem and stored in parenchyma cells — chiefly phloem parenchyma, and also the general parenchyma of the cortex, pith and medullary rays.
Photosynthesis in the leaf mesophyll produces organic food substances that the plant needs to move to non-photosynthetic parts and hold in reserve until they are needed. Two things happen in sequence: transport, and then storage.
- Transport is carried out by the phloem, whose sieve tubes conduct the dissolved organic food from the leaves (the source) to other regions of the plant (the sinks). …
Method: Tracing the Journey from Source to Sink, Then Asking Where It Stops
Rather than naming the storage tissue directly, trace the entire journey of a sugar molecule from where it is made to where it ends up, and ask specifically what kind of cell would make sense as a "parking spot" along that route.
Step 1 — where is the sugar made? In the leaf mesophyll, during photosynthesis (the "source").
Step 2 — how does it travel? It enters the phloem's sieve tubes, which conduct the dissolved sugar to other parts of the plant (the "sinks") — roots, developing fruits, storage organs, growing tissue.
Step 3 — what happens once it "arrives"? The sieve tube itself is not a storage compartment — a sieve tube element has no nucleus and minimal organelles; it is built purely as a conducting pipe, not a warehouse. So the sugar must be handed off to some OTHER cell type once it reaches its destination (or even along the way, for local use). …
- AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQQ.Choose the incorrect statements of the following A) Parenchyma constitute major components of plant organs B) The anatomy of seed plants was published by Easu C) Protophloem will have broader sieve tubes D) Sieve tube functions are controlled by its nucleus (A) A, B (B) C, D (C) A, D (D) B, D
›Reveal solutionSolution
Protophloem sieve tubes are narrower (not broader) than metaphloem's, and sieve tubes lack their own nucleus (function is controlled by the companion cell) — these two statements are the incorrect ones.
Concept and Intuition
Parenchyma is indeed the most abundant, least specialised ground tissue making up the bulk of most plant organs, and Katherine Esau's landmark textbook "Anatomy of Seed Plants" (1965) is the standard reference on plant internal anatomy — both true. Phloem tissue matures progressively: the first-formed protophloem has narrow, short-lived sieve elements, while the later metaphloem develops wider, longer-lasting sieve tubes. Mature sieve tube elements lose their nucleus entirely at functional maturity, so their metabolic activities are directed by the nucleus of their associated companion cell instead.
Step-by-Step Solution
- Statement A: TRUE — parenchyma is the dominant, unspecialised tissue making up most of the volume of plant organs.
- Statement B: TRUE — "Anatomy of Seed Plants" is indeed authored by Katherine Esau, a foundational plant anatomy reference. …
- AP EAPCET 2025Set ap-2025-05-19-AN1 markMCQQ.Assertion (A) : The functions of sieve tubes are controlled by the nucleus of companion cells. The companion cells help in maintaining the pressure gradient in sieve tubes. Reason (R) : Gymnosperms phloem have albuminous cells and sieve cells. Identify the correct option from the following (A) (A) and (R) are true. (R) is correct explanation for (A) (B) (A) and (R) are true. But (R) is not correct explanation for (A) (C) (A) is true, but (R) is false (D) (A) is false, but (R) is true
›Reveal solutionSolution
Both statements are factually correct but describe two unrelated (angiosperm vs gymnosperm) phloem facts, so (R) does not explain (A) — option (B).
Concept and Intuition
In angiosperms, mature sieve tube elements lose their nucleus and rely on the adjoining, nucleated companion cell to regulate their metabolic activities and maintain pressure gradients for translocation. Gymnosperms lack sieve tubes/companion cells altogether, having the more primitive sieve cells and albuminous cells instead.
Step-by-Step Solution
- Assertion: sieve tube function is controlled by the companion cell nucleus, which also helps maintain the pressure gradient — this is a standard, correct fact about angiosperm phloem.
- Reason: gymnosperm phloem has albuminous cells and sieve cells (instead of companion cells and sieve tubes) — also a correct, standard fact, but about a different group of plants (gymnosperms, not angiosperms). …
- AP EAPCET 2023Set ap-2023-05-23-AN1 markMCQQ.This type of cells are not present in phloem of a monocot stem (A) Phloem parenchyma. (B) Sieve tubes. (C) Companion cells. (D) Phloem fibres.
›Reveal solutionSolution
This tests a specific anatomical distinguishing feature of monocot phloem — the absence of phloem parenchyma.
Concept and Intuition
Phloem tissue generally comprises sieve tubes, companion cells, phloem parenchyma, and phloem fibres. However, in the vascular bundles of most monocotyledonous stems, phloem parenchyma is characteristically absent — this is one of the standard anatomical criteria used to distinguish monocot from dicot stem structure.
Step-by-Step Solution
- Recall the four components of typical phloem: sieve tubes, companion cells, phloem parenchyma, phloem fibres.
- Recall the anatomical rule specific to monocot stems: phloem parenchyma is missing, while sieve tubes and companion cells are present (functional conducting elements), and phloem fibres may also be present as sclerenchymatous support. …
- AP EAPCET 2021Set ap-2021-09-03-AN1 markMCQQ.Which statement is correct? (A) Phloem fibres are absent in most monocot (B) Phloem parenchyma are absent in most monocot (C) Phloem fibres absent in the primary phloem (D) Phloem fibres absent in the secondary phloem
›Reveal solutionSolution
Phloem parenchyma is the phloem element absent in most monocotyledons.
Concept and Intuition
Phloem is a complex tissue made of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Phloem fibres (bast fibres) are the sclerenchymatous, non-conducting supporting cells. Phloem parenchyma are thin-walled living cells that store food and other substances.
Step-by-Step Solution
- Recall that phloem fibres are generally absent in the primary phloem but present in the secondary phloem — so statements (C) and (D) are reversed/incorrect.
- Phloem parenchyma is composed of elongated, tapering living cells; it is present in dicots but is characteristically absent in most monocotyledons.
- Statement (A) wrongly claims phloem fibres are absent in monocots — fibres are common in monocot phloem.
- Hence only statement (B) is correct.
Common Mistakes
- Confusing phloem parenchyma (absent in monocots) with phloem fibres. …
- AP EAPCET 2021Set ap-2021-09-03-FN1 markMCQQ.Phloem parenchyma is absent in ____ (A) Dicot stem (B) Dicot leaf (C) Monocot stem (D) Dicot root
›Reveal solutionSolution
Monocot stem phloem characteristically lacks phloem parenchyma, unlike dicot phloem. Answer: (C).
Concept and Intuition
Phloem is composed of sieve elements, companion cells, phloem parenchyma, and phloem fibres. Phloem parenchyma cells store food materials such as starch and resins and conduct some lateral transport. This component varies between plant groups: dicotyledonous plants (stems, leaves, and roots) generally have phloem parenchyma as part of their vascular bundles. Monocotyledonous stems, however, have a distinctive anatomy (closed, scattered vascular bundles) in which phloem parenchyma is typically absent — a commonly tested anatomical distinguishing feature between monocot and dicot vascular tissue.
Step-by-Step Solution
- Recall the standard anatomical distinguishing features of monocot vs dicot vascular bundles.
- Dicot stem, dicot leaf, and dicot root phloem generally include phloem parenchyma among their components.
- Monocot stems, in contrast, are noted specifically for lacking phloem parenchyma in their vascular bundles. …
- AP EAPCET 2021Set ap-2021-09-07-FN1 markMCQQ.Assertion (A): Sieve tube are enucleated cells. Reason (R): The functions of sieve tubes are controlled by Phloem Parenchyma (A) Both A and R are correct (B) Both A and R are not correct (C) A is correct but R is wrong (D) A is wrong but R is correct
›Reveal solutionSolution
Sieve tubes are indeed enucleate (A correct), but it is companion cells — not phloem parenchyma — that regulate them (R wrong); answer (C).
Concept and Intuition
Phloem has four elements: sieve tubes, companion cells, phloem parenchyma, and phloem fibres. Sieve tube elements lose their nucleus at maturity yet remain living, and their functioning (loading/unloading of photosynthate, maintaining pressure flow) is sustained by the adjacent, nucleate companion cells, which are physically connected to them by numerous plasmodesmata/pit connections and arise from the same mother cell during development. Phloem parenchyma is a distinct, separate storage/packing tissue in the phloem — it is not specifically wired to control sieve tube function the way companion cells are.
Step-by-Step Solution
- Assess the Assertion: Sieve tube elements are enucleate at maturity — this is a well-established, correct fact. …
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