SA I - Full Biology Test 1 - Class 10 MCQ

Our learning (intelligence) depends on cerebrum. which is a part of the forebrain (prosencephalon).

Medulla Oblongata and Involuntary Functions:
- The medulla oblongata is a part of the brainstem located between the pons and the spinal cord.
- It is responsible for regulating and controlling many involuntary functions of the body.
- The medulla oblongata plays a crucial role in maintaining vital bodily functions such as:
- Breathing: It controls the rate and depth of breathing by regulating the respiratory centers.
- Heart rate: It regulates the heart rate and blood pressure through its control over the cardiac centers.
- Swallowing and digestion: It coordinates the muscles involved in swallowing and controls the secretion of digestive enzymes.
- Vomiting and coughing: It triggers the reflex actions of vomiting and coughing when necessary.
- Reflexes: It controls various reflex actions, including sneezing, blinking, and gagging.
- Damage or injury to the medulla oblongata can result in severe disruptions to these involuntary functions, leading to life-threatening conditions.
- Therefore, it is true that the medulla oblongata controls involuntary functions of the body.

The oxygen in photosynthesis is released from:
- H₂O (Water)
Photosynthesis is the process by which plants, algae, and some bacteria convert sunlight, carbon dioxide (CO₂), and water (H₂O) into glucose (carbohydrate) and oxygen (O₂). The oxygen released during photosynthesis is derived from water molecules.
Here is a detailed explanation of the process:
1. Light Energy Absorption:
- Chlorophyll, a pigment found in chloroplasts of plant cells, absorbs light energy from the sun.
2. Splitting of Water Molecules:
- This light energy is used to split water molecules (H₂O) into hydrogen ions (H+) and oxygen (O₂) atoms through a process called photolysis.
3. Electron Transport Chain:
- The hydrogen ions generated from the splitting of water are used in the electron transport chain to produce energy-rich molecules such as ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).
4. Carbon Dioxide Fixation:
- Carbon dioxide (CO₂) from the atmosphere enters the plant through small openings called stomata and is converted into glucose through a series of enzymatic reactions known as the Calvin cycle.
5. Release of Oxygen:
- As water is split during photosynthesis, oxygen atoms are released into the atmosphere as a byproduct. This oxygen is the same oxygen that we breathe.
Thus, the oxygen released during photosynthesis is derived from the water molecule (H₂O) and not from carbon dioxide (CO₂), carbohydrate, or chlorophyll.

Each stoma is guarded by:
- Guard cells: These specialized cells surround the stomatal pore and regulate its opening and closing. They control the exchange of gases and water vapor between the plant and the environment by altering their shape and volume.
- Palisade cells: These cells are found in the upper layer of the leaf and are responsible for photosynthesis. They contain chloroplasts and are densely packed to maximize light absorption.
- Mesophyll cells: These cells are found in the inner layer of the leaf and are involved in photosynthesis and gas exchange. They contain chloroplasts and are loosely packed, allowing for the diffusion of gases.
- Parenchyma cells: These are the most common type of plant cells and are involved in various functions such as storage, photosynthesis, and support.
Explanation:
- Stomata are tiny openings found on the surface of leaves and stems that allow for gas exchange and transpiration in plants.
- Each stoma is surrounded by two specialized cells called guard cells.
- The guard cells can change their shape and volume to control the opening and closing of the stomatal pore.
- When the guard cells are turgid (swollen with water), they become curved and the stomatal pore opens, allowing for the exchange of gases and water vapor.
- When the guard cells lose water and become flaccid, they straighten up and the stomatal pore closes, preventing excessive water loss.
- The other cell types mentioned (palisade cells, mesophyll cells, and parenchyma cells) are all important for the overall functioning of the leaf but do not directly guard the stomata.

Photosynthesis proceeds in sequence of:
- Light phase and dark phase
- Light phase alone
- Light phase and dark phase
- Dark phase alone
Answer: C. Light phase and dark phase
Detailed
Photosynthesis, the process by which plants convert sunlight into chemical energy, occurs in two main phases: the light phase (also known as the light-dependent phase) and the dark phase (also known as the light-independent phase or the Calvin cycle). Here is a detailed explanation of the sequence:
1. Light Phase:
- It takes place in the thylakoid membrane of the chloroplast.
- Requires sunlight as an energy source.
- Involves the following steps:
- Absorption of light energy by chlorophyll and other pigments.
- Conversion of light energy into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).
- Splitting of water molecules (photolysis) to release oxygen gas as a byproduct.
- The light phase produces energy-rich molecules (ATP and NADPH) that will be used in the dark phase.
2. Dark Phase:
- It takes place in the stroma of the chloroplast.
- Does not require direct sunlight but relies on the energy-rich molecules (ATP and NADPH) produced in the light phase.
- Involves the following steps:
- Carbon fixation: Incorporation of carbon dioxide (CO2) into organic compounds, particularly a three-carbon molecule called PGA (phosphoglyceric acid).
- Reduction: Conversion of PGA into G3P (glyceraldehyde-3-phosphate) using ATP and NADPH.
- Regeneration: Some G3P molecules are used to regenerate the starting molecule (RuBP) for the carbon fixation process.
- The dark phase results in the production of glucose and other organic compounds, which can be used by the plant for growth and metabolism.
Therefore, photosynthesis proceeds in a sequence of both the light phase and the dark phase. The light phase harnesses energy from sunlight and converts it into chemical energy, while the dark phase uses this energy to fix carbon dioxide and produce glucose. Both phases are essential for the overall process of photosynthesis.

Reaction occurs inside stroma of chloroplasts where light energy is not captured
The reaction that occurs inside the stroma of chloroplasts where light energy is not captured is known as the dark reaction or the Calvin cycle. This process takes place in the absence of light and is responsible for the synthesis of glucose molecules from carbon dioxide.
Key points:
- The dark reaction is also known as the light-independent reaction or the carbon fixation phase.
- It takes place in the stroma, which is the fluid-filled space inside the chloroplasts.
- The dark reaction does not directly require light energy for its functioning.
- The primary goal of this reaction is to convert carbon dioxide molecules into glucose through a series of enzymatic reactions.
- The dark reaction utilizes ATP and NADPH, which are products of the light-dependent reactions, to power the synthesis of glucose.
- The Calvin cycle consists of three main stages: carbon fixation, reduction, and regeneration of RuBP (ribulose bisphosphate).
- The end product of the dark reaction is glucose, which can be used for energy storage or converted into other organic molecules.
- The dark reaction is essential for the overall process of photosynthesis as it provides the necessary building blocks for plant growth and metabolism.
Overall, the dark reaction occurring inside the stroma of chloroplasts plays a crucial role in the synthesis of glucose and the overall process of photosynthesis.

Grana are present inside:
- Mitochondria: Grana are not found inside mitochondria. Mitochondria are responsible for energy production in the cell.
- Golgi bodies: Grana are not found inside Golgi bodies. Golgi bodies are responsible for modifying, sorting, and packaging proteins and lipids for transport.
- Chloroplast: Grana are found inside chloroplasts. Chloroplasts are the site of photosynthesis in plant cells, and grana are the stacks of thylakoid membranes where the light-dependent reactions of photosynthesis occur. They contain the pigments necessary for capturing and converting light energy into chemical energy.
- Ribosome: Grana are not found inside ribosomes. Ribosomes are responsible for protein synthesis in the cell.
Therefore, the correct answer is C: Chloroplast.

Function of Leaf in a Plant:
The leaf is an essential part of a plant and performs various functions necessary for the plant's survival and growth. Some of the key functions of leaves include:
1. Photosynthesis:
- Leaves are the primary site for photosynthesis, the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen.
- Chlorophyll, located in the chloroplasts of leaf cells, captures sunlight energy and initiates the photosynthetic reactions.
2. Transpiration:
- Leaves play a crucial role in transpiration, the process by which plants lose water vapor through small openings called stomata.
- Transpiration helps in the absorption and transportation of water and nutrients from the roots to other parts of the plant.
3. Respiration:
- Leaves also play a role in respiration, the process by which plants convert glucose and oxygen into energy, carbon dioxide, and water.
- Respiration occurs in the mitochondria of leaf cells and is essential for the plant's metabolic activities.
4. Gas Exchange:
- Leaves have stomata, which allow for the exchange of gases such as oxygen and carbon dioxide between the plant and the atmosphere.
- This gas exchange is vital for the plant's ability to take in carbon dioxide for photosynthesis and release oxygen as a byproduct.
5. Storage:
- Some leaves, such as those of succulent plants, can store water and nutrients, helping the plant survive during periods of drought or nutrient scarcity.
6. Protection:
- Leaf structures like trichomes, thorns, and tough epidermal layers provide protection against herbivores, excessive sunlight, and mechanical damage.
In conclusion, the function of the leaf in a plant is multifaceted. It is primarily involved in photosynthesis, transpiration, and respiration, but also facilitates gas exchange, storage, and protection. All of these functions are critical for the plant's growth, development, and survival. Therefore, the correct answer to the given question is option D: All the above.

Chlorophyll and its presence in various organisms:
Chlorophyll is a pigment found in plants and other photosynthetic organisms. It plays a crucial role in the process of photosynthesis, where it absorbs light energy and converts it into chemical energy.
Chlorophyll is present in:
- Algae: Algae are photosynthetic organisms that can be found in both marine and freshwater environments. They contain chlorophyll, which allows them to use sunlight to produce energy.
- Bacteria: Certain types of bacteria, such as cyanobacteria, also contain chlorophyll. These bacteria can perform photosynthesis and are often found in aquatic environments.
- Croton: Croton is a genus of flowering plants that belong to the family Euphorbiaceae. Some species within this genus, such as Croton lechleri, contain chlorophyll and are capable of photosynthesis.
- Both (A) and (C): Therefore, the correct answer is option D, as chlorophyll is present in both algae and certain species of Croton plants.
In summary, chlorophyll is a pigment found in a variety of organisms, including algae, bacteria, and certain species of Croton plants. These organisms utilize chlorophyll to capture light energy and carry out the process of photosynthesis.

The reflex arc in the reflex action is formed by:
The reflex arc is a neural pathway that controls reflex actions. It involves the following components:
1. Receptor:
- The receptor is a sensory organ that detects a stimulus and converts it into an electrical signal.
- It can be located in various parts of the body, such as the skin, muscles, or organs.
2. Sensory Neuron:
- The sensory neuron carries the electrical signal from the receptor to the central nervous system (CNS), which consists of the brain and spinal cord.
- It transmits the signal as an action potential.
3. Interneuron:
- In the spinal cord, the sensory neuron connects with an interneuron.
- The interneuron relays the signal from the sensory neuron to the motor neuron.
4. Motor Neuron:
- The motor neuron carries the electrical signal from the CNS to the effector, which is usually a muscle or gland.
- It transmits the signal as an action potential.
5. Effector:
- The effector responds to the signal by producing a reflex action.
- In the case of a muscle, it contracts, and in the case of a gland, it secretes a hormone or other substances.
6. Reflex Action:
- The reflex action is an automatic and involuntary response to a stimulus.
- It occurs without conscious thought and helps protect the body from harm or maintain homeostasis.
Therefore, the correct sequence of components in the reflex arc is: Receptor - Sensory Neuron - Interneuron - Motor Neuron - Effector. The reflex arc does not involve the brain directly, as the reflex action is controlled at the spinal cord level.

Light Phase of Photosynthesis: Formation of ATP and NADPH
The light phase of photosynthesis, also known as the light-dependent reactions, occurs in the thylakoid membrane of the chloroplast. This phase involves the absorption of light energy by chlorophyll and the subsequent conversion of that energy into chemical energy in the form of ATP and NADPH.
1. Formation of ATP:
- Light energy is absorbed by chlorophyll molecules in the thylakoid membrane.
- This energy is used to split water molecules into hydrogen ions (H+) and oxygen (O2) through a process called photolysis.
- The electrons released from the water molecules are captured by an electron carrier called NADP+ (nicotinamide adenine dinucleotide phosphate), which gets reduced to NADPH.
- As the electrons move through a series of electron carriers in the thylakoid membrane, they release energy that is used to pump protons (H+) across the membrane, creating a proton gradient.
- The proton gradient drives the synthesis of ATP through a process called chemiosmosis, where ATP synthase enzyme utilizes the energy of the proton gradient to produce ATP from ADP (adenosine diphosphate) and inorganic phosphate (Pi).
2. Formation of NADPH:
- The electrons captured by NADP+ during photolysis combine with hydrogen ions (H+) to form NADPH.
- NADPH is an electron carrier that is used in the later stages of photosynthesis to reduce carbon dioxide and produce carbohydrates during the dark phase (Calvin cycle).
3. Formation of Both ATP and NADPH:
- The light phase of photosynthesis involves both the generation of ATP through chemiosmosis and the formation of NADPH through the reduction of NADP+.
- These two energy-rich compounds, ATP and NADPH, are essential for the dark phase of photosynthesis (Calvin cycle) where they provide the necessary energy and reducing power to convert carbon dioxide into carbohydrates.
Conclusion:
In the light phase of photosynthesis, both ATP and NADPH are formed. ATP is generated through chemiosmosis, utilizing the energy of the proton gradient created by the movement of electrons through the electron transport chain. NADPH is formed by the reduction of NADP+ using the electrons released during photolysis. These energy-rich molecules play a crucial role in the synthesis of carbohydrates during the dark phase of photosynthesis.

Answer:
The junction of two neurons is called a synapse. Here is a detailed explanation:
Synapse:
- A synapse is a specialized junction where two neurons come into close proximity to transmit information.
- It is the point of communication between two neurons or between a neuron and an effector cell (such as a muscle or gland).
- The synapse allows for the transmission of signals from one neuron to another, enabling the functioning of the nervous system.
Function of Synapse:
- The synapse is responsible for the transmission of electrical or chemical signals between neurons.
- It allows for the integration and processing of information in the nervous system.
- It enables the transfer of information from sensory neurons to motor neurons, allowing for the initiation of appropriate responses.
Components of a Synapse:
- Presynaptic Neuron: The neuron that sends the signal.
- Postsynaptic Neuron: The neuron that receives the signal.
- Synaptic Cleft: The small gap between the presynaptic and postsynaptic neurons.
- Neurotransmitters: Chemical messengers released by the presynaptic neuron into the synaptic cleft.
- Receptors: Proteins on the postsynaptic neuron that bind to neurotransmitters and initiate a response.
Types of Synapses:
- Chemical Synapse: The most common type of synapse, where neurotransmitters are released into the synaptic cleft to transmit signals.
- Electrical Synapse: A less common type of synapse, where electrical signals pass directly between neurons through gap junctions.
In conclusion, the junction of two neurons is called a synapse. It is a specialized structure that allows for the transmission of signals in the nervous system.

The Cerebral Hemispheres:
The cerebral hemispheres are the largest part of the brain and are responsible for various functions related to thinking, interpreting sensory information, and controlling voluntary movements. They are divided into two halves, the left hemisphere and the right hemisphere, which are connected by a thick band of nerve fibers called the corpus callosum.
Functions of the Cerebral Hemispheres:
The cerebral hemispheres are the centers for numerous functions, including:
1. Thinking:
- The cerebral hemispheres play a crucial role in complex cognitive processes such as thinking, reasoning, problem-solving, and decision-making.
- They are involved in higher-order mental functions like perception, attention, memory, and language processing.
2. Sensory Perception:
- The cerebral hemispheres receive and interpret sensory information from the environment.
- They are responsible for processing visual, auditory, tactile, and other sensory inputs.
3. Motor Control:
- The cerebral hemispheres are involved in the planning and execution of voluntary movements.
- They control the coordination, timing, and precision of movements.
4. Language Processing:
- The left hemisphere, in most individuals, is dominant for language processing.
- It is responsible for understanding and producing spoken and written language.
5. Emotion and Behavior:
- The cerebral hemispheres are involved in regulating emotions, mood, and behavior.
- They play a role in emotional responses, social interactions, and personality traits.
6. Spatial Awareness:
- The cerebral hemispheres contribute to spatial awareness and the ability to navigate and orient oneself in the environment.
Conclusion:
In summary, the cerebral hemispheres are responsible for a wide range of functions, including thinking, sensory perception, motor control, language processing, emotion and behavior regulation, and spatial awareness. They are essential for our ability to understand and interact with the world around us.