Generation of net ATP molecule(s) during Cellular respiration without involving mitochondria occurs during:

📌Concept:
-Cellular respiration can be defined as the metabolic process by which complex organic substances are broken down into simple products. 
-During this process, energy is released that is stored in energy-carrying biomolecules called ATP. This energy is later utilized to carry out other metabolic activities.
-In eukaryotic cells, mitochondria play an important role in ATP synthesis.
-The enzymes required for ATP synthesis are present in the mitochondria.
-However, the generation of ATP also takes place in certain processes without involving mitochondria such as in glycolysis.

✅Explanation:
Option 1: Krebs cycle – INCORRECT
-​Krebs cycle also known as the TCA cycle is part of aerobic respiration.
-It provides energy to cells in the form of ATP.
-It takes place in the matrix of mitochondria.
Option 2: Electron Transport Chain – INCORRECT
-Electron Transport Chain is the third step during aerobic respiration and involves the formation of the water molecule and ATP.
-ETS takes place in the inner mitochondrial membrane.
-NADH2 and FADH2 produced during the initial steps of aerobic respiration – glycolysis, connecting link reaction, and Kreb's cycle- are oxidized in ETC with the help of various electron carriers and enzymes.
Option 3: Substrate-level Phosphorylation – CORRECT
-​Substrate-level Phosphorylation is a chemical reaction in which ATP is synthesized by direct transfer of phosphate group from an intermediate molecule to ADP.
-Substrate-level Phosphorylation is seen during the process of glycolysis.
-Glycolysis is the first step in both aerobic and anaerobic respiration.
-It takes place in the cytoplasm without the use of oxygen.
-During glycolysis 2 ATP molecules are produced.
-These ATP molecules are formed without the involvement of mitochondria.
Option 4: Photorespiration – INCORRECT
-​Photorespiration occurs in photosynthetic plants.
-Photorespiration can be defined as a light-dependent process in which the photosynthetic organs of a plant utilize oxygen and release carbon dioxide.
-Photorespiration is considered to be a wasteful process. This is because 25% of photosynthetically fixed carbon dioxide is lost in this process.
-It takes place in several organelles – chloroplast, peroxisome and mitochondria.
-At the end of the photorespiration CO2 and ammonia are released. No ATP is produced in this process.