All questions of Cell Discovery and Theory for Grade 9 Exam

Explanation:
Statement 1: The cisternae in Golgi complex have cis face and trans face.
The Golgi complex is an organelle found in eukaryotic cells that plays a key role in the processing and sorting of proteins and lipids. It consists of a series of flattened membrane-bound sacs called cisternae. These cisternae have two distinct faces - the cis face and the trans face.

Statement 2: The cis face is also called the forming face and the trans face is also called the maturing face.
The cis face of the Golgi complex is the side that is closest to the endoplasmic reticulum (ER), where newly synthesized proteins and lipids enter the Golgi. It is involved in receiving and sorting proteins and lipids from the ER. The cis face is also referred to as the forming face because it is where the Golgi complex receives and forms vesicles containing these proteins and lipids.

The trans face of the Golgi complex is the side that is farthest from the ER. It is involved in packaging proteins and lipids into vesicles that will be transported to their final destinations. The trans face is also referred to as the maturing face because it is where the Golgi complex modifies and matures these proteins and lipids before they are packaged into vesicles.

Conclusion:
Both statements 1 and 2 are correct, but statement 2 is not the correct explanation of statement 1. The cis face and trans face of the Golgi complex are indeed referred to as the forming face and maturing face, respectively, but these terms do not explain the function or location of the two faces. The cis face is where the Golgi complex receives and forms vesicles, while the trans face is where it packages and matures proteins and lipids. Therefore, the correct option is B.

Cell Structure of a Plant Cell

Introduction
A plant cell is a eukaryotic cell that makes up the structural and functional unit of plants. It contains various organelles that perform specific functions necessary for the cell's survival and growth. In this context, let's analyze the given options to identify the wrong statement regarding the structure of a plant cell.

Analysis of Statements
a) Cellulosic cell wall is present inside the cell membrane.
- This statement is incorrect. The cell wall is located outside the cell membrane in a plant cell. It provides rigidity, protection, and support to the cell. The primary component of the plant cell wall is cellulose, a complex carbohydrate.

b) Centrioles are usually absent.
- This statement is correct. Unlike animal cells, plant cells do not have centrioles. Centrioles are involved in cellular division and the formation of the spindle apparatus during mitosis. Plant cells undergo cell division through a different mechanism, and hence, centrioles are not present.

c) A large central vacuole is present.
- This statement is correct. Plant cells typically contain a large central vacuole that occupies a significant portion of the cell's volume. The vacuole is enclosed by a membrane called the tonoplast and plays a crucial role in maintaining cell turgidity, storing water, nutrients, and waste products.

d) Golgi apparatus is formed of a number of unconnected units called dictyosomes.
- This statement is correct. The Golgi apparatus in plant cells is composed of a stack of flattened, membrane-bound sacs called dictyosomes. These dictyosomes function in processing, modifying, and packaging proteins and lipids for transport to various destinations within and outside the cell.

Conclusion
Therefore, the wrong statement with respect to the structure of a plant cell is option 'A' - "Cellulosic cell wall is present inside the cell membrane." The cell wall is located outside the cell membrane in a plant cell.

The Energy Currency of Eukaryotic Cells
In eukaryotic cells, the primary energy currency is ATP (adenosine triphosphate), which is generated in the mitochondria. Let's explore why the correct answer is option 'D', which identifies mitochondria as a double-membraned organelle.
Mitochondria Structure
- Mitochondria are unique because they possess two membranes:
- Outer Membrane: Smooth and permeable to small molecules.
- Inner Membrane: Highly folded into structures called cristae, which increase surface area for ATP production.
Site of ATP Production
- The inner membrane contains the electron transport chain (ETC) and ATP synthase, crucial components of cellular respiration.
- Process of ATP Generation:
- Glycolysis occurs in the cytosol, breaking down glucose into pyruvate.
- Krebs Cycle takes place in the mitochondrial matrix, generating electron carriers.
- Oxidative Phosphorylation occurs across the inner membrane, where the ETC generates a proton gradient used by ATP synthase to produce ATP.
Importance of Double Membrane
- The double membrane structure is vital for compartmentalizing the mitochondrial functions:
- Isolation of Enzymes: Different enzymes and substrates are localized in specific areas, optimizing metabolic processes.
- Proton Gradient Formation: The separation allows for efficient creation of the proton motive force necessary for ATP synthesis.
Conclusion
Thus, the double-membraned nature of mitochondria is integral to their role as the energy powerhouse of eukaryotic cells. This structure supports the necessary biochemical processes that culminate in ATP production, making it the correct answer to the question regarding the energy currency of the cell.

Smooth Endoplasmic Reticulum and Steroid Synthesis
The smooth endoplasmic reticulum (SER) is a specialized organelle within the cell responsible for various functions, one of which includes the synthesis of steroids.

Steroid Synthesis in Smooth Endoplasmic Reticulum
- The SER contains enzymes that are involved in the synthesis of lipids, including steroids.
- Steroids are a type of lipid that play important roles in various physiological processes such as hormone signaling, regulation of metabolism, and immune response.
- The enzymes present in the SER help in the production of steroids from precursor molecules.
- This synthesis process involves a series of enzymatic reactions that convert precursor molecules into steroid hormones such as cortisol, estrogen, and testosterone.

Other Functions of Smooth Endoplasmic Reticulum
- In addition to steroid synthesis, the SER is also involved in the metabolism of drugs and detoxification processes in the liver.
- It plays a role in the synthesis of lipids and phospholipids, which are essential components of cell membranes.
- The SER is also involved in the storage and release of calcium ions, which are important for muscle contraction and cell signaling.

Conclusion
In conclusion, smooth endoplasmic reticulum is well developed in synthesizing steroids due to the presence of specialized enzymes that facilitate the production of these important lipid molecules.